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 $58.48   13.308%   $66.2625   $66.26   $66.25   $66.30  
  Purchase #2 $170.66   13.152%   $193.1052   $193.11   $193.10   $193.10  
  Purchase #3 $91.84   8.762%   $99.887   $99.89   $99.90   $99.90  
  Purchase #4 $59.65   6.369%   $63.4491   $63.45   $63.45   $63.40  
  Purchase #5 $119.91   7.215%   $128.5615   $128.56   $128.55   $128.60  
  Purchase #6 $245.75   6.141%   $260.8415   $260.84   $260.85   $260.80  
  Purchase #7 $88.33   10.652%   $97.7389   $97.74   $97.75   $97.70  
  7 purchase totals = $834.62       $909.8457   $909.85   $909.85   $909.80