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 $98.33   6.702%   $104.9201   $104.92   $104.90   $104.90  
  Purchase #2 $244.61   8.605%   $265.6587   $265.66   $265.65   $265.70  
  Purchase #3 $56.46   12.375%   $63.4469   $63.45   $63.45   $63.40  
  Purchase #4 $85.58   9.535%   $93.7401   $93.74   $93.75   $93.70  
  Purchase #5 $188.73   3.591%   $195.5073   $195.51   $195.50   $195.50  
  Purchase #6 $47.93   6.340%   $50.9688   $50.97   $50.95   $51.00  
  Purchase #7 $91.28   8.369%   $98.9192   $98.92   $98.90   $98.90  
  7 purchase totals = $812.92       $873.1611   $873.17   $873.10   $873.10