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 $58.83   12.493%   $66.1796   $66.18   $66.20   $66.20  
  Purchase #2 $241.38   4.383%   $251.9597   $251.96   $251.95   $252.00  
  Purchase #3 $40.89   11.420%   $45.5596   $45.56   $45.55   $45.60  
  Purchase #4 $74.48   3.132%   $76.8127   $76.81   $76.80   $76.80  
  Purchase #5 $11.97   3.373%   $12.3737   $12.37   $12.35   $12.40  
  Purchase #6 $247.42   10.408%   $273.1715   $273.17   $273.15   $273.20  
  Purchase #7 $5.72   12.237%   $6.42   $6.42   $6.40   $6.40  
  7 purchase totals = $680.69       $732.4768   $732.47   $732.40   $732.60