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 $219.93   11.839%   $245.9675   $245.97   $245.95   $246.00  
  Purchase #2 $136.62   12.499%   $153.6961   $153.70   $153.70   $153.70  
  Purchase #3 $94.85   9.395%   $103.7612   $103.76   $103.75   $103.80  
  Purchase #4 $100.74   9.733%   $110.545   $110.55   $110.55   $110.50  
  Purchase #5 $16.77   11.506%   $18.6996   $18.70   $18.70   $18.70  
  Purchase #6 $192.92   3.657%   $199.9751   $199.98   $200.00   $200.00  
  Purchase #7 $144.47   6.799%   $154.2925   $154.29   $154.30   $154.30  
  7 purchase totals = $906.30       $986.9370   $986.95   $986.95   $987.00