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 $93.71   10.697%   $103.7342   $103.73   $103.75   $103.70  
  Purchase #2 $57.46   5.636%   $60.6984   $60.70   $60.70   $60.70  
  Purchase #3 $26.38   4.302%   $27.5149   $27.51   $27.50   $27.50  
  Purchase #4 $114.56   7.496%   $123.1474   $123.15   $123.15   $123.10  
  Purchase #5 $166.36   11.407%   $185.3367   $185.34   $185.35   $185.30  
  Purchase #6 $204.87   12.431%   $230.3374   $230.34   $230.35   $230.30  
  Purchase #7 $242.61   8.579%   $263.4235   $263.42   $263.40   $263.40  
  7 purchase totals = $905.95       $994.1925   $994.19   $994.20   $994.00