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 $119.78   5.121%   $125.9139   $125.91   $125.90   $125.90  
  Purchase #2 $178.56   11.343%   $198.8141   $198.81   $198.80   $198.80  
  Purchase #3 $32.81   7.596%   $35.3022   $35.30   $35.30   $35.30  
  Purchase #4 $14.30   7.593%   $15.3858   $15.39   $15.40   $15.40  
  Purchase #5 $166.34   7.336%   $178.5427   $178.54   $178.55   $178.50  
  Purchase #6 $97.34   12.291%   $109.3041   $109.30   $109.30   $109.30  
  Purchase #7 $211.38   13.480%   $239.874   $239.87   $239.85   $239.90  
  7 purchase totals = $820.51       $903.1368   $903.12   $903.10   $903.10