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 $50.38   6.702%   $53.7565   $53.76   $53.75   $53.80  
  Purchase #2 $142.96   4.399%   $149.2488   $149.25   $149.25   $149.20  
  Purchase #3 $188.72   11.534%   $210.487   $210.49   $210.50   $210.50  
  Purchase #4 $33.65   6.794%   $35.9362   $35.94   $35.95   $35.90  
  Purchase #5 $244.92   11.761%   $273.725   $273.73   $273.75   $273.70  
  Purchase #6 $81.71   8.265%   $88.4633   $88.46   $88.45   $88.50  
  Purchase #7 $84.57   13.625%   $96.0927   $96.09   $96.10   $96.10  
  7 purchase totals = $826.91       $907.7095   $907.72   $907.75   $907.70