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 $198.72   13.312%   $225.1736   $225.17   $225.15   $225.20  
  Purchase #2 $126.53   13.858%   $144.0645   $144.06   $144.05   $144.10  
  Purchase #3 $219.29   3.305%   $226.5375   $226.54   $226.55   $226.50  
  Purchase #4 $70.49   9.390%   $77.109   $77.11   $77.10   $77.10  
  Purchase #5 $73.61   6.794%   $78.6111   $78.61   $78.60   $78.60  
  Purchase #6 $76.28   11.197%   $84.8211   $84.82   $84.80   $84.80  
  Purchase #7 $119.78   4.560%   $125.242   $125.24   $125.25   $125.20  
  7 purchase totals = $884.70       $961.5588   $961.55   $961.50   $961.50