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 $83.96   3.483%   $86.8843   $86.88   $86.90   $86.90  
  Purchase #2 $36.32   10.144%   $40.0043   $40.00   $40.00   $40.00  
  Purchase #3 $117.32   13.103%   $132.6924   $132.69   $132.70   $132.70  
  Purchase #4 $196.96   7.807%   $212.3367   $212.34   $212.35   $212.30  
  Purchase #5 $244.43   13.432%   $277.2618   $277.26   $277.25   $277.30  
  Purchase #6 $142.40   11.285%   $158.4698   $158.47   $158.45   $158.50  
  Purchase #7 $147.60   8.172%   $159.6619   $159.66   $159.65   $159.70  
  7 purchase totals = $968.99       $1,067.3112   $1,067.30   $1,067.30   $1,067.40