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 $222.35   8.723%   $241.7456   $241.75   $241.75   $241.70  
  Purchase #2 $25.96   6.419%   $27.6264   $27.63   $27.65   $27.60  
  Purchase #3 $27.95   8.127%   $30.2215   $30.22   $30.20   $30.20  
  Purchase #4 $20.86   5.298%   $21.9652   $21.97   $21.95   $22.00  
  Purchase #5 $66.75   5.127%   $70.1723   $70.17   $70.15   $70.20  
  Purchase #6 $104.70   7.261%   $112.3023   $112.30   $112.30   $112.30  
  Purchase #7 $217.64   4.301%   $227.0007   $227.00   $227.00   $227.00  
  7 purchase totals = $686.21       $731.0340   $731.04   $731.00   $731.00