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 $220.82   10.739%   $244.5339   $244.53   $244.55   $244.50  
  Purchase #2 $107.36   8.858%   $116.8699   $116.87   $116.85   $116.90  
  Purchase #3 $139.43   8.786%   $151.6803   $151.68   $151.70   $151.70  
  Purchase #4 $87.33   4.399%   $91.1716   $91.17   $91.15   $91.20  
  Purchase #5 $53.83   13.193%   $60.9318   $60.93   $60.95   $60.90  
  Purchase #6 $245.85   9.603%   $269.459   $269.46   $269.45   $269.50  
  Purchase #7 $6.60   9.403%   $7.2206   $7.22   $7.20   $7.20  
  7 purchase totals = $861.22       $941.8671   $941.86   $941.85   $941.90