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 $191.66   8.108%   $207.1998   $207.20   $207.20   $207.20  
  Purchase #2 $172.81   13.352%   $195.8836   $195.88   $195.90   $195.90  
  Purchase #3 $79.76   8.819%   $86.794   $86.79   $86.80   $86.80  
  Purchase #4 $215.31   8.829%   $234.3197   $234.32   $234.30   $234.30  
  Purchase #5 $55.62   6.495%   $59.2325   $59.23   $59.25   $59.20  
  Purchase #6 $30.86   10.246%   $34.0219   $34.02   $34.00   $34.00  
  Purchase #7 $92.85   3.420%   $96.0255   $96.03   $96.05   $96.00  
  7 purchase totals = $838.87       $913.4770   $913.47   $913.50   $913.40