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 $126.38   13.452%   $143.3806   $143.38   $143.40   $143.40  
  Purchase #2 $248.95   12.646%   $280.4322   $280.43   $280.45   $280.40  
  Purchase #3 $119.96   8.735%   $130.4385   $130.44   $130.45   $130.40  
  Purchase #4 $87.85   9.116%   $95.8584   $95.86   $95.85   $95.90  
  Purchase #5 $154.28   4.345%   $160.9835   $160.98   $161.00   $161.00  
  Purchase #6 $199.87   4.480%   $208.8242   $208.82   $208.80   $208.80  
  Purchase #7 $6.66   4.622%   $6.9678   $6.97   $6.95   $7.00  
  7 purchase totals = $943.95       $1,026.8852   $1,026.88   $1,026.90   $1,026.90