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 $81.60   13.131%   $92.3149   $92.31   $92.30   $92.30  
  Purchase #2 $55.36   4.798%   $58.0162   $58.02   $58.00   $58.00  
  Purchase #3 $186.92   10.617%   $206.7653   $206.77   $206.75   $206.80  
  Purchase #4 $42.98   9.208%   $46.9376   $46.94   $46.95   $46.90  
  Purchase #5 $54.43   5.414%   $57.3768   $57.38   $57.40   $57.40  
  Purchase #6 $234.42   11.580%   $261.5658   $261.57   $261.55   $261.60  
  Purchase #7 $141.51   7.429%   $152.0228   $152.02   $152.00   $152.00  
  7 purchase totals = $797.22       $874.9994   $875.01   $874.95   $875.00