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 $83.59   10.639%   $92.4831   $92.48   $92.50   $92.50  
  Purchase #2 $149.67   13.420%   $169.7557   $169.76   $169.75   $169.80  
  Purchase #3 $48.82   13.800%   $55.5572   $55.56   $55.55   $55.60  
  Purchase #4 $96.88   11.360%   $107.8856   $107.89   $107.90   $107.90  
  Purchase #5 $60.50   12.197%   $67.8792   $67.88   $67.90   $67.90  
  Purchase #6 $153.85   8.736%   $167.2903   $167.29   $167.30   $167.30  
  Purchase #7 $163.85   7.232%   $175.6996   $175.70   $175.70   $175.70  
  7 purchase totals = $757.16       $836.5507   $836.56   $836.60   $836.70