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 $248.49   7.461%   $267.0298   $267.03   $267.05   $267.00  
  Purchase #2 $195.85   4.183%   $204.0424   $204.04   $204.05   $204.00  
  Purchase #3 $89.32   8.676%   $97.0694   $97.07   $97.05   $97.10  
  Purchase #4 $17.98   8.132%   $19.4421   $19.44   $19.45   $19.40  
  Purchase #5 $167.51   8.676%   $182.0432   $182.04   $182.05   $182.00  
  Purchase #6 $223.32   10.579%   $246.945   $246.95   $246.95   $246.90  
  Purchase #7 $196.61   10.566%   $217.3838   $217.38   $217.40   $217.40  
  7 purchase totals = $1,139.08       $1,233.9557   $1,233.95   $1,234.00   $1,233.80