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 $32.69   12.165%   $36.6667   $36.67   $36.65   $36.70  
  Purchase #2 $246.38   8.466%   $267.2385   $267.24   $267.25   $267.20  
  Purchase #3 $88.78   6.382%   $94.4459   $94.45   $94.45   $94.40  
  Purchase #4 $238.43   4.183%   $248.4035   $248.40   $248.40   $248.40  
  Purchase #5 $23.91   12.306%   $26.8524   $26.85   $26.85   $26.90  
  Purchase #6 $82.99   3.750%   $86.1021   $86.10   $86.10   $86.10  
  Purchase #7 $198.97   13.398%   $225.628   $225.63   $225.65   $225.60  
  7 purchase totals = $912.15       $985.3371   $985.34   $985.35   $985.30