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 $38.63   3.132%   $39.8399   $39.84   $39.85   $39.80  
  Purchase #2 $236.50   4.272%   $246.6033   $246.60   $246.60   $246.60  
  Purchase #3 $84.47   13.269%   $95.6783   $95.68   $95.70   $95.70  
  Purchase #4 $89.81   3.578%   $93.0234   $93.02   $93.00   $93.00  
  Purchase #5 $240.65   12.452%   $270.6157   $270.62   $270.60   $270.60  
  Purchase #6 $83.92   4.364%   $87.5823   $87.58   $87.60   $87.60  
  Purchase #7 $118.76   8.529%   $128.889   $128.89   $128.90   $128.90  
  7 purchase totals = $892.74       $962.2319   $962.23   $962.25   $962.20