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 $90.71   8.685%   $98.5882   $98.59   $98.60   $98.60  
  Purchase #2 $104.97   11.265%   $116.7949   $116.79   $116.80   $116.80  
  Purchase #3 $65.71   3.703%   $68.1432   $68.14   $68.15   $68.10  
  Purchase #4 $167.77   9.464%   $183.6478   $183.65   $183.65   $183.60  
  Purchase #5 $122.28   12.207%   $137.2067   $137.21   $137.20   $137.20  
  Purchase #6 $45.73   5.765%   $48.3663   $48.37   $48.35   $48.40  
  Purchase #7 $159.92   6.747%   $170.7098   $170.71   $170.70   $170.70  
  7 purchase totals = $757.09       $823.4569   $823.46   $823.45   $823.40