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 $72.85   13.371%   $82.5908   $82.59   $82.60   $82.60  
  Purchase #2 $141.25   11.558%   $157.5757   $157.58   $157.60   $157.60  
  Purchase #3 $70.50   7.741%   $75.9574   $75.96   $75.95   $76.00  
  Purchase #4 $233.85   4.701%   $244.8433   $244.84   $244.85   $244.80  
  Purchase #5 $136.42   4.380%   $142.3952   $142.40   $142.40   $142.40  
  Purchase #6 $158.66   8.845%   $172.6935   $172.69   $172.70   $172.70  
  Purchase #7 $71.61   10.799%   $79.3432   $79.34   $79.35   $79.30  
  7 purchase totals = $885.14       $955.3991   $955.40   $955.45   $955.40