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 $64.60   5.586%   $68.2086   $68.21   $68.20   $68.20  
  Purchase #2 $185.98   10.197%   $204.9444   $204.94   $204.95   $204.90  
  Purchase #3 $22.30   7.678%   $24.0122   $24.01   $24.00   $24.00  
  Purchase #4 $51.26   7.716%   $55.2152   $55.22   $55.20   $55.20  
  Purchase #5 $103.74   9.148%   $113.2301   $113.23   $113.25   $113.20  
  Purchase #6 $117.28   6.559%   $124.9724   $124.97   $124.95   $125.00  
  Purchase #7 $250.37   4.806%   $262.4028   $262.40   $262.40   $262.40  
  7 purchase totals = $795.53       $852.9857   $852.98   $852.95   $852.90