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 $92.30   3.603%   $95.6256   $95.63   $95.65   $95.60  
  Purchase #2 $22.76   4.550%   $23.7956   $23.80   $23.80   $23.80  
  Purchase #3 $234.69   10.537%   $259.4193   $259.42   $259.40   $259.40  
  Purchase #4 $143.97   10.226%   $158.6924   $158.69   $158.70   $158.70  
  Purchase #5 $62.61   10.582%   $69.2354   $69.24   $69.25   $69.20  
  Purchase #6 $250.64   6.606%   $267.1973   $267.20   $267.20   $267.20  
  Purchase #7 $6.27   9.178%   $6.8455   $6.85   $6.85   $6.80  
  7 purchase totals = $813.24       $880.8111   $880.83   $880.85   $880.70