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 $48.25   11.162%   $53.6357   $53.64   $53.65   $53.60  
  Purchase #2 $154.53   7.593%   $166.2635   $166.26   $166.25   $166.30  
  Purchase #3 $149.32   9.106%   $162.9171   $162.92   $162.90   $162.90  
  Purchase #4 $48.87   7.522%   $52.546   $52.55   $52.55   $52.50  
  Purchase #5 $232.71   4.180%   $242.4373   $242.44   $242.45   $242.40  
  Purchase #6 $99.77   8.637%   $108.3871   $108.39   $108.40   $108.40  
  Purchase #7 $20.50   8.189%   $22.1787   $22.18   $22.20   $22.20  
  7 purchase totals = $753.95       $808.3654   $808.38   $808.40   $808.30