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 $110.61   12.866%   $124.8411   $124.84   $124.85   $124.80  
  Purchase #2 $209.66   3.648%   $217.3084   $217.31   $217.30   $217.30  
  Purchase #3 $226.45   3.752%   $234.9464   $234.95   $234.95   $234.90  
  Purchase #4 $66.71   13.610%   $75.7892   $75.79   $75.80   $75.80  
  Purchase #5 $10.48   4.597%   $10.9618   $10.96   $10.95   $11.00  
  Purchase #6 $241.87   8.726%   $262.9756   $262.98   $263.00   $263.00  
  Purchase #7 $173.49   5.470%   $182.9799   $182.98   $183.00   $183.00  
  7 purchase totals = $1,039.27       $1,109.8024   $1,109.81   $1,109.85   $1,109.80