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 $240.77   8.134%   $260.3542   $260.35   $260.35   $260.40  
  Purchase #2 $101.90   7.303%   $109.3418   $109.34   $109.35   $109.30  
  Purchase #3 $57.77   5.498%   $60.9462   $60.95   $60.95   $60.90  
  Purchase #4 $72.62   11.677%   $81.0998   $81.10   $81.10   $81.10  
  Purchase #5 $59.79   7.524%   $64.2886   $64.29   $64.30   $64.30  
  Purchase #6 $175.26   10.567%   $193.7797   $193.78   $193.80   $193.80  
  Purchase #7 $89.90   10.314%   $99.1723   $99.17   $99.15   $99.20  
  7 purchase totals = $798.01       $868.9826   $868.98   $869.00   $869.00