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 $87.34   8.149%   $94.4573   $94.46   $94.45   $94.50  
  Purchase #2 $131.45   3.603%   $136.1861   $136.19   $136.20   $136.20  
  Purchase #3 $182.55   6.427%   $194.2825   $194.28   $194.30   $194.30  
  Purchase #4 $228.67   7.357%   $245.4933   $245.49   $245.50   $245.50  
  Purchase #5 $209.43   9.484%   $229.2923   $229.29   $229.30   $229.30  
  Purchase #6 $143.25   5.352%   $150.9167   $150.92   $150.90   $150.90  
  Purchase #7 $246.54   11.847%   $275.7476   $275.75   $275.75   $275.70  
  7 purchase totals = $1,229.23       $1,326.3758   $1,326.38   $1,326.40   $1,326.40