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 $91.36   13.866%   $104.028   $104.03   $104.05   $104.00  
  Purchase #2 $49.49   4.201%   $51.5691   $51.57   $51.55   $51.60  
  Purchase #3 $86.97   11.811%   $97.242   $97.24   $97.25   $97.20  
  Purchase #4 $234.38   7.401%   $251.7265   $251.73   $251.75   $251.70  
  Purchase #5 $63.46   6.555%   $67.6198   $67.62   $67.60   $67.60  
  Purchase #6 $108.70   9.624%   $119.1613   $119.16   $119.15   $119.20  
  Purchase #7 $229.94   11.428%   $256.2175   $256.22   $256.20   $256.20  
  7 purchase totals = $864.30       $947.5642   $947.57   $947.55   $947.50