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 $209.96   11.794%   $234.7227   $234.72   $234.70   $234.70  
  Purchase #2 $87.67   6.432%   $93.3089   $93.31   $93.30   $93.30  
  Purchase #3 $14.78   4.187%   $15.3988   $15.40   $15.40   $15.40  
  Purchase #4 $40.82   13.358%   $46.2727   $46.27   $46.25   $46.30  
  Purchase #5 $174.50   3.532%   $180.6633   $180.66   $180.65   $180.70  
  Purchase #6 $125.61   11.347%   $139.863   $139.86   $139.85   $139.90  
  Purchase #7 $223.44   10.522%   $246.9504   $246.95   $246.95   $247.00  
  7 purchase totals = $876.78       $957.1798   $957.17   $957.10   $957.30