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 $243.55   7.559%   $261.9599   $261.96   $261.95   $262.00  
  Purchase #2 $185.41   12.341%   $208.2914   $208.29   $208.30   $208.30  
  Purchase #3 $87.35   7.381%   $93.7973   $93.80   $93.80   $93.80  
  Purchase #4 $111.37   12.640%   $125.4472   $125.45   $125.45   $125.40  
  Purchase #5 $149.41   3.697%   $154.9337   $154.93   $154.95   $154.90  
  Purchase #6 $84.89   9.519%   $92.9707   $92.97   $92.95   $93.00  
  Purchase #7 $27.95   9.277%   $30.5429   $30.54   $30.55   $30.50  
  7 purchase totals = $889.93       $967.9431   $967.94   $967.95   $967.90