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 $112.86   10.291%   $124.4744   $124.47   $124.45   $124.50  
  Purchase #2 $44.26   5.715%   $46.7895   $46.79   $46.80   $46.80  
  Purchase #3 $168.32   3.588%   $174.3593   $174.36   $174.35   $174.40  
  Purchase #4 $119.28   12.431%   $134.1077   $134.11   $134.10   $134.10  
  Purchase #5 $49.97   10.106%   $55.02   $55.02   $55.00   $55.00  
  Purchase #6 $190.38   7.629%   $204.9041   $204.90   $204.90   $204.90  
  Purchase #7 $237.82   7.556%   $255.7897   $255.79   $255.80   $255.80  
  7 purchase totals = $922.89       $995.4447   $995.44   $995.40   $995.50