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 $181.66   7.504%   $195.2918   $195.29   $195.30   $195.30  
  Purchase #2 $235.86   10.253%   $260.0427   $260.04   $260.05   $260.00  
  Purchase #3 $239.32   11.117%   $265.9252   $265.93   $265.95   $265.90  
  Purchase #4 $152.60   3.834%   $158.4507   $158.45   $158.45   $158.50  
  Purchase #5 $75.53   9.655%   $82.8224   $82.82   $82.80   $82.80  
  Purchase #6 $134.27   5.197%   $141.248   $141.25   $141.25   $141.20  
  Purchase #7 $234.75   8.174%   $253.9385   $253.94   $253.95   $253.90  
  7 purchase totals = $1,253.99       $1,357.7193   $1,357.72   $1,357.75   $1,357.60