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 $68.87   13.625%   $78.2535   $78.25   $78.25   $78.30  
  Purchase #2 $175.40   11.521%   $195.6078   $195.61   $195.60   $195.60  
  Purchase #3 $86.37   12.817%   $97.44   $97.44   $97.45   $97.40  
  Purchase #4 $218.80   12.262%   $245.6293   $245.63   $245.65   $245.60  
  Purchase #5 $5.46   10.790%   $6.0491   $6.05   $6.05   $6.00  
  Purchase #6 $53.27   11.394%   $59.3396   $59.34   $59.35   $59.30  
  Purchase #7 $133.90   7.353%   $143.7457   $143.75   $143.75   $143.70  
  7 purchase totals = $742.07       $826.0650   $826.07   $826.10   $825.90