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 $62.53   13.152%   $70.7539   $70.75   $70.75   $70.80  
  Purchase #2 $115.41   9.270%   $126.1085   $126.11   $126.10   $126.10  
  Purchase #3 $203.25   5.195%   $213.8088   $213.81   $213.80   $213.80  
  Purchase #4 $8.94   11.152%   $9.937   $9.94   $9.95   $9.90  
  Purchase #5 $195.78   7.190%   $209.8566   $209.86   $209.85   $209.90  
  Purchase #6 $93.86   11.431%   $104.5891   $104.59   $104.60   $104.60  
  Purchase #7 $157.28   6.114%   $166.8961   $166.90   $166.90   $166.90  
  7 purchase totals = $837.05       $901.9500   $901.96   $901.95   $902.00