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 $92.93   5.680%   $98.2084   $98.21   $98.20   $98.20  
  Purchase #2 $185.71   10.223%   $204.6951   $204.70   $204.70   $204.70  
  Purchase #3 $95.33   8.518%   $103.4502   $103.45   $103.45   $103.50  
  Purchase #4 $52.93   13.288%   $59.9633   $59.96   $59.95   $60.00  
  Purchase #5 $206.42   13.736%   $234.7739   $234.77   $234.75   $234.80  
  Purchase #6 $206.28   3.707%   $213.9268   $213.93   $213.95   $213.90  
  Purchase #7 $10.87   12.102%   $12.1855   $12.19   $12.20   $12.20  
  7 purchase totals = $850.47       $927.2032   $927.21   $927.20   $927.30