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 $239.49   9.107%   $261.3004   $261.30   $261.30   $261.30  
  Purchase #2 $215.55   12.610%   $242.7309   $242.73   $242.75   $242.70  
  Purchase #3 $179.34   7.671%   $193.0972   $193.10   $193.10   $193.10  
  Purchase #4 $5.48   5.291%   $5.7699   $5.77   $5.75   $5.80  
  Purchase #5 $235.31   4.175%   $245.1342   $245.13   $245.15   $245.10  
  Purchase #6 $237.89   8.661%   $258.4937   $258.49   $258.50   $258.50  
  Purchase #7 $195.68   4.753%   $204.9807   $204.98   $205.00   $205.00  
  7 purchase totals = $1,308.74       $1,411.5070   $1,411.50   $1,411.55   $1,411.50