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 $226.81   5.650%   $239.6248   $239.62   $239.60   $239.60  
  Purchase #2 $38.30   4.600%   $40.0618   $40.06   $40.05   $40.10  
  Purchase #3 $113.76   10.604%   $125.8231   $125.82   $125.80   $125.80  
  Purchase #4 $241.33   4.660%   $252.576   $252.58   $252.60   $252.60  
  Purchase #5 $250.82   9.784%   $275.3602   $275.36   $275.35   $275.40  
  Purchase #6 $18.67   3.331%   $19.2919   $19.29   $19.30   $19.30  
  Purchase #7 $62.69   12.433%   $70.4842   $70.48   $70.50   $70.50  
  7 purchase totals = $952.38       $1,023.2220   $1,023.21   $1,023.20   $1,023.30