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 $202.25   10.774%   $224.0404   $224.04   $224.05   $224.00  
  Purchase #2 $199.59   13.136%   $225.8081   $225.81   $225.80   $225.80  
  Purchase #3 $220.71   11.319%   $245.6922   $245.69   $245.70   $245.70  
  Purchase #4 $16.44   3.636%   $17.0378   $17.04   $17.05   $17.00  
  Purchase #5 $125.83   8.310%   $136.2865   $136.29   $136.30   $136.30  
  Purchase #6 $65.38   13.451%   $74.1743   $74.17   $74.15   $74.20  
  Purchase #7 $46.60   3.296%   $48.1359   $48.14   $48.15   $48.10  
  7 purchase totals = $876.80       $971.1752   $971.18   $971.20   $971.10