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 $206.71   9.462%   $226.2689   $226.27   $226.25   $226.30  
  Purchase #2 $236.86   4.225%   $246.8673   $246.87   $246.85   $246.90  
  Purchase #3 $221.97   6.301%   $235.9563   $235.96   $235.95   $236.00  
  Purchase #4 $244.95   12.423%   $275.3801   $275.38   $275.40   $275.40  
  Purchase #5 $112.84   13.203%   $127.7383   $127.74   $127.75   $127.70  
  Purchase #6 $108.96   12.792%   $122.8982   $122.90   $122.90   $122.90  
  Purchase #7 $6.87   6.837%   $7.3397   $7.34   $7.35   $7.30  
  7 purchase totals = $1,139.16       $1,242.4488   $1,242.46   $1,242.45   $1,242.50