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 $224.84   11.472%   $250.6336   $250.63   $250.65   $250.60  
  Purchase #2 $211.38   13.707%   $240.3539   $240.35   $240.35   $240.40  
  Purchase #3 $21.45   4.849%   $22.4901   $22.49   $22.50   $22.50  
  Purchase #4 $102.51   3.873%   $106.4802   $106.48   $106.50   $106.50  
  Purchase #5 $109.66   3.679%   $113.6944   $113.69   $113.70   $113.70  
  Purchase #6 $221.98   12.602%   $249.9539   $249.95   $249.95   $250.00  
  Purchase #7 $86.53   13.103%   $97.868   $97.87   $97.85   $97.90  
  7 purchase totals = $978.35       $1,081.4741   $1,081.46   $1,081.50   $1,081.60