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 $204.43   8.457%   $221.7186   $221.72   $221.70   $221.70  
  Purchase #2 $201.94   4.280%   $210.583   $210.58   $210.60   $210.60  
  Purchase #3 $49.68   5.746%   $52.5346   $52.53   $52.55   $52.50  
  Purchase #4 $120.69   4.299%   $125.8785   $125.88   $125.90   $125.90  
  Purchase #5 $103.40   11.522%   $115.3137   $115.31   $115.30   $115.30  
  Purchase #6 $240.65   13.651%   $273.5011   $273.50   $273.50   $273.50  
  Purchase #7 $108.61   5.631%   $114.7258   $114.73   $114.75   $114.70  
  7 purchase totals = $1,029.40       $1,114.2553   $1,114.25   $1,114.30   $1,114.20