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 $93.65   11.770%   $104.6726   $104.67   $104.65   $104.70  
  Purchase #2 $58.28   3.681%   $60.4253   $60.43   $60.45   $60.40  
  Purchase #3 $175.41   12.410%   $197.1784   $197.18   $197.20   $197.20  
  Purchase #4 $124.46   10.527%   $137.5619   $137.56   $137.55   $137.60  
  Purchase #5 $238.56   10.328%   $263.1985   $263.20   $263.20   $263.20  
  Purchase #6 $36.73   5.227%   $38.6499   $38.65   $38.65   $38.60  
  Purchase #7 $67.51   12.618%   $76.0284   $76.03   $76.05   $76.00  
  7 purchase totals = $794.60       $877.7150   $877.72   $877.75   $877.70