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 $183.97   8.333%   $199.3002   $199.30   $199.30   $199.30  
  Purchase #2 $220.84   9.340%   $241.4665   $241.47   $241.45   $241.50  
  Purchase #3 $93.47   10.734%   $103.5031   $103.50   $103.50   $103.50  
  Purchase #4 $32.96   13.741%   $37.489   $37.49   $37.50   $37.50  
  Purchase #5 $242.90   4.262%   $253.2524   $253.25   $253.25   $253.30  
  Purchase #6 $5.82   12.565%   $6.5513   $6.55   $6.55   $6.60  
  Purchase #7 $88.28   8.323%   $95.6275   $95.63   $95.65   $95.60  
  7 purchase totals = $868.24       $937.1900   $937.19   $937.20   $937.30