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 $70.58   8.118%   $76.3097   $76.31   $76.30   $76.30  
  Purchase #2 $208.86   13.378%   $236.8013   $236.80   $236.80   $236.80  
  Purchase #3 $92.76   4.471%   $96.9073   $96.91   $96.90   $96.90  
  Purchase #4 $7.49   10.752%   $8.2953   $8.30   $8.30   $8.30  
  Purchase #5 $94.33   12.285%   $105.9184   $105.92   $105.90   $105.90  
  Purchase #6 $113.63   9.197%   $124.0806   $124.08   $124.10   $124.10  
  Purchase #7 $151.89   5.532%   $160.2926   $160.29   $160.30   $160.30  
  7 purchase totals = $739.54       $808.6052   $808.61   $808.60   $808.60