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 $62.86   6.156%   $66.7297   $66.73   $66.75   $66.70  
  Purchase #2 $40.73   4.168%   $42.4276   $42.43   $42.45   $42.40  
  Purchase #3 $11.38   11.270%   $12.6625   $12.66   $12.65   $12.70  
  Purchase #4 $70.76   7.289%   $75.9177   $75.92   $75.90   $75.90  
  Purchase #5 $227.66   3.411%   $235.4255   $235.43   $235.45   $235.40  
  Purchase #6 $209.54   9.635%   $229.7292   $229.73   $229.75   $229.70  
  Purchase #7 $28.75   13.818%   $32.7227   $32.72   $32.70   $32.70  
  7 purchase totals = $651.68       $695.6149   $695.62   $695.65   $695.50