Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.88   11.518%   $271.9701   $271.97   $271.95   $272.00  
  Purchase #2 $151.97   6.438%   $161.7538   $161.75   $161.75   $161.80  
  Purchase #3 $85.72   4.115%   $89.2474   $89.25   $89.25   $89.20  
  Purchase #4 $204.53   7.190%   $219.2357   $219.24   $219.25   $219.20  
  Purchase #5 $207.96   9.451%   $227.6143   $227.61   $227.60   $227.60  
  Purchase #6 $119.44   9.315%   $130.5658   $130.57   $130.55   $130.60  
  Purchase #7 $137.88   4.422%   $143.9771   $143.98   $144.00   $144.00  
  7 purchase totals = $1,151.38       $1,244.3642   $1,244.37   $1,244.35   $1,244.40