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 $66.75   3.317%   $68.9641   $68.96   $68.95   $69.00  
  Purchase #2 $137.81   11.490%   $153.6444   $153.64   $153.65   $153.60  
  Purchase #3 $158.78   3.529%   $164.3833   $164.38   $164.40   $164.40  
  Purchase #4 $68.77   9.843%   $75.539   $75.54   $75.55   $75.50  
  Purchase #5 $126.44   10.452%   $139.6555   $139.66   $139.65   $139.70  
  Purchase #6 $24.42   12.620%   $27.5018   $27.50   $27.50   $27.50  
  Purchase #7 $248.45   3.610%   $257.419   $257.42   $257.40   $257.40  
  7 purchase totals = $831.42       $887.1071   $887.10   $887.10   $887.10