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 $54.76   6.695%   $58.4262   $58.43   $58.45   $58.40  
  Purchase #2 $117.81   6.391%   $125.3392   $125.34   $125.35   $125.30  
  Purchase #3 $53.66   6.490%   $57.1425   $57.14   $57.15   $57.10  
  Purchase #4 $250.78   8.169%   $271.2662   $271.27   $271.25   $271.30  
  Purchase #5 $205.28   8.874%   $223.4965   $223.50   $223.50   $223.50  
  Purchase #6 $98.44   4.652%   $103.0194   $103.02   $103.00   $103.00  
  Purchase #7 $107.36   10.121%   $118.2259   $118.23   $118.25   $118.20  
  7 purchase totals = $888.09       $956.9159   $956.93   $956.95   $956.80