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 $54.95   11.427%   $61.2291   $61.23   $61.25   $61.20  
  Purchase #2 $218.54   3.289%   $225.7278   $225.73   $225.75   $225.70  
  Purchase #3 $17.95   3.138%   $18.5133   $18.51   $18.50   $18.50  
  Purchase #4 $178.38   7.501%   $191.7603   $191.76   $191.75   $191.80  
  Purchase #5 $46.78   13.532%   $53.1103   $53.11   $53.10   $53.10  
  Purchase #6 $220.92   6.662%   $235.6377   $235.64   $235.65   $235.60  
  Purchase #7 $75.75   8.520%   $82.2039   $82.20   $82.20   $82.20  
  7 purchase totals = $813.27       $868.1824   $868.18   $868.20   $868.10