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 $205.79   10.422%   $227.2374   $227.24   $227.25   $227.20  
  Purchase #2 $116.33   3.111%   $119.949   $119.95   $119.95   $119.90  
  Purchase #3 $165.39   4.611%   $173.0161   $173.02   $173.00   $173.00  
  Purchase #4 $90.42   5.189%   $95.1119   $95.11   $95.10   $95.10  
  Purchase #5 $22.55   10.766%   $24.9777   $24.98   $25.00   $25.00  
  Purchase #6 $223.97   9.338%   $244.8843   $244.88   $244.90   $244.90  
  Purchase #7 $56.67   6.394%   $60.2935   $60.29   $60.30   $60.30  
  7 purchase totals = $881.12       $945.4699   $945.47   $945.50   $945.40