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 $185.97   11.844%   $207.9963   $208.00   $208.00   $208.00  
  Purchase #2 $199.73   6.456%   $212.6246   $212.62   $212.60   $212.60  
  Purchase #3 $126.84   5.631%   $133.9824   $133.98   $134.00   $134.00  
  Purchase #4 $232.28   8.459%   $251.9286   $251.93   $251.95   $251.90  
  Purchase #5 $197.68   9.819%   $217.0902   $217.09   $217.10   $217.10  
  Purchase #6 $69.86   7.698%   $75.2378   $75.24   $75.25   $75.20  
  Purchase #7 $246.45   4.391%   $257.2716   $257.27   $257.25   $257.30  
  7 purchase totals = $1,258.81       $1,356.1315   $1,356.13   $1,356.15   $1,356.10