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 $206.75   9.559%   $226.5132   $226.51   $226.50   $226.50  
  Purchase #2 $185.78   9.147%   $202.7733   $202.77   $202.75   $202.80  
  Purchase #3 $67.96   12.292%   $76.3136   $76.31   $76.30   $76.30  
  Purchase #4 $66.93   13.428%   $75.9174   $75.92   $75.90   $75.90  
  Purchase #5 $97.67   5.452%   $102.995   $103.00   $103.00   $103.00  
  Purchase #6 $166.85   8.733%   $181.421   $181.42   $181.40   $181.40  
  Purchase #7 $32.45   11.601%   $36.2145   $36.21   $36.20   $36.20  
  7 purchase totals = $824.39       $902.1480   $902.14   $902.05   $902.10