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 $69.57   4.689%   $72.8321   $72.83   $72.85   $72.80  
  Purchase #2 $229.68   13.276%   $260.1723   $260.17   $260.15   $260.20  
  Purchase #3 $17.63   8.451%   $19.1199   $19.12   $19.10   $19.10  
  Purchase #4 $21.90   8.642%   $23.7926   $23.79   $23.80   $23.80  
  Purchase #5 $5.30   13.556%   $6.0185   $6.02   $6.00   $6.00  
  Purchase #6 $153.60   9.581%   $168.3164   $168.32   $168.30   $168.30  
  Purchase #7 $176.45   12.673%   $198.8115   $198.81   $198.80   $198.80  
  7 purchase totals = $674.13       $749.0633   $749.06   $749.00   $749.00