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 $52.69   8.717%   $57.283   $57.28   $57.30   $57.30  
  Purchase #2 $112.94   3.341%   $116.7133   $116.71   $116.70   $116.70  
  Purchase #3 $14.64   5.188%   $15.3995   $15.40   $15.40   $15.40  
  Purchase #4 $178.67   8.503%   $193.8623   $193.86   $193.85   $193.90  
  Purchase #5 $15.36   10.259%   $16.9358   $16.94   $16.95   $16.90  
  Purchase #6 $227.31   7.850%   $245.1538   $245.15   $245.15   $245.20  
  Purchase #7 $44.41   3.556%   $45.9892   $45.99   $46.00   $46.00  
  7 purchase totals = $646.02       $691.3369   $691.33   $691.35   $691.40