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 $58.55   10.568%   $64.7376   $64.74   $64.75   $64.70  
  Purchase #2 $219.71   6.258%   $233.4595   $233.46   $233.45   $233.50  
  Purchase #3 $114.37   3.236%   $118.071   $118.07   $118.05   $118.10  
  Purchase #4 $229.33   7.115%   $245.6468   $245.65   $245.65   $245.60  
  Purchase #5 $14.61   10.659%   $16.1673   $16.17   $16.15   $16.20  
  Purchase #6 $79.56   3.575%   $82.4043   $82.40   $82.40   $82.40  
  Purchase #7 $196.29   4.680%   $205.4764   $205.48   $205.50   $205.50  
  7 purchase totals = $912.42       $965.9629   $965.97   $965.95   $966.00