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 $44.83   11.574%   $50.0186   $50.02   $50.00   $50.00  
  Purchase #2 $61.81   12.339%   $69.4367   $69.44   $69.45   $69.40  
  Purchase #3 $231.61   5.655%   $244.7075   $244.71   $244.70   $244.70  
  Purchase #4 $95.43   5.707%   $100.8762   $100.88   $100.90   $100.90  
  Purchase #5 $93.59   12.806%   $105.5751   $105.58   $105.60   $105.60  
  Purchase #6 $197.34   13.730%   $224.4348   $224.43   $224.45   $224.40  
  Purchase #7 $149.28   7.155%   $159.961   $159.96   $159.95   $160.00  
  7 purchase totals = $873.89       $955.0099   $955.02   $955.05   $955.00