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 $235.53   4.462%   $246.0393   $246.04   $246.05   $246.00  
  Purchase #2 $53.67   8.762%   $58.3726   $58.37   $58.35   $58.40  
  Purchase #3 $245.75   11.450%   $273.8884   $273.89   $273.90   $273.90  
  Purchase #4 $126.78   4.749%   $132.8008   $132.80   $132.80   $132.80  
  Purchase #5 $79.35   7.821%   $85.556   $85.56   $85.55   $85.60  
  Purchase #6 $250.29   4.247%   $260.9198   $260.92   $260.90   $260.90  
  Purchase #7 $149.90   7.301%   $160.8442   $160.84   $160.85   $160.80  
  7 purchase totals = $1,141.27       $1,218.4211   $1,218.42   $1,218.40   $1,218.40