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 $58.67   12.553%   $66.0348   $66.03   $66.05   $66.00  
  Purchase #2 $147.55   5.784%   $156.0843   $156.08   $156.10   $156.10  
  Purchase #3 $40.92   10.519%   $45.2244   $45.22   $45.20   $45.20  
  Purchase #4 $231.33   5.794%   $244.7333   $244.73   $244.75   $244.70  
  Purchase #5 $59.35   5.164%   $62.4148   $62.41   $62.40   $62.40  
  Purchase #6 $105.87   10.565%   $117.0552   $117.06   $117.05   $117.10  
  Purchase #7 $175.63   10.153%   $193.4617   $193.46   $193.45   $193.50  
  7 purchase totals = $819.32       $885.0085   $884.99   $885.00   $885.00