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 $213.91   13.109%   $241.9515   $241.95   $241.95   $242.00  
  Purchase #2 $64.93   7.341%   $69.6965   $69.70   $69.70   $69.70  
  Purchase #3 $79.87   4.192%   $83.2182   $83.22   $83.20   $83.20  
  Purchase #4 $41.93   6.344%   $44.59   $44.59   $44.60   $44.60  
  Purchase #5 $94.99   11.125%   $105.5576   $105.56   $105.55   $105.60  
  Purchase #6 $166.95   6.822%   $178.3393   $178.34   $178.35   $178.30  
  Purchase #7 $175.59   7.455%   $188.6802   $188.68   $188.70   $188.70  
  7 purchase totals = $838.17       $912.0333   $912.04   $912.05   $912.10