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 $193.49   13.505%   $219.6208   $219.62   $219.60   $219.60  
  Purchase #2 $118.37   9.255%   $129.3251   $129.33   $129.35   $129.30  
  Purchase #3 $73.72   3.826%   $76.5405   $76.54   $76.55   $76.50  
  Purchase #4 $164.87   13.208%   $186.646   $186.65   $186.65   $186.60  
  Purchase #5 $33.30   8.590%   $36.1605   $36.16   $36.15   $36.20  
  Purchase #6 $71.97   4.746%   $75.3857   $75.39   $75.40   $75.40  
  Purchase #7 $96.49   6.800%   $103.0513   $103.05   $103.05   $103.10  
  7 purchase totals = $752.21       $826.7299   $826.74   $826.75   $826.70