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 $26.63   11.639%   $29.7295   $29.73   $29.75   $29.70  
  Purchase #2 $57.55   5.190%   $60.5368   $60.54   $60.55   $60.50  
  Purchase #3 $53.97   12.373%   $60.6477   $60.65   $60.65   $60.60  
  Purchase #4 $226.26   7.601%   $243.458   $243.46   $243.45   $243.50  
  Purchase #5 $85.76   3.262%   $88.5575   $88.56   $88.55   $88.60  
  Purchase #6 $62.58   12.625%   $70.4807   $70.48   $70.50   $70.50  
  Purchase #7 $159.49   3.176%   $164.5554   $164.56   $164.55   $164.60  
  7 purchase totals = $672.24       $717.9656   $717.98   $718.00   $718.00