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 $135.25   6.201%   $143.6369   $143.64   $143.65   $143.60  
  Purchase #2 $112.71   12.596%   $126.907   $126.91   $126.90   $126.90  
  Purchase #3 $233.38   9.588%   $255.7565   $255.76   $255.75   $255.80  
  Purchase #4 $91.50   10.644%   $101.2393   $101.24   $101.25   $101.20  
  Purchase #5 $5.26   7.690%   $5.6645   $5.66   $5.65   $5.70  
  Purchase #6 $116.81   10.613%   $129.207   $129.21   $129.20   $129.20  
  Purchase #7 $91.56   6.622%   $97.6231   $97.62   $97.60   $97.60  
  7 purchase totals = $786.47       $860.0343   $860.04   $860.00   $860.00