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 $70.94   5.794%   $75.0503   $75.05   $75.05   $75.10  
  Purchase #2 $241.41   3.667%   $250.2625   $250.26   $250.25   $250.30  
  Purchase #3 $52.36   8.763%   $56.9483   $56.95   $56.95   $56.90  
  Purchase #4 $95.27   6.185%   $101.1624   $101.16   $101.15   $101.20  
  Purchase #5 $204.92   4.698%   $214.5471   $214.55   $214.55   $214.50  
  Purchase #6 $14.48   8.664%   $15.7345   $15.73   $15.75   $15.70  
  Purchase #7 $191.90   9.844%   $210.7906   $210.79   $210.80   $210.80  
  7 purchase totals = $871.28       $924.4957   $924.49   $924.50   $924.50