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 $57.48   8.670%   $62.4635   $62.46   $62.45   $62.50  
  Purchase #2 $102.71   9.346%   $112.3093   $112.31   $112.30   $112.30  
  Purchase #3 $50.46   11.578%   $56.3023   $56.30   $56.30   $56.30  
  Purchase #4 $168.53   11.287%   $187.552   $187.55   $187.55   $187.60  
  Purchase #5 $106.97   7.367%   $114.8505   $114.85   $114.85   $114.90  
  Purchase #6 $245.26   3.338%   $253.4468   $253.45   $253.45   $253.40  
  Purchase #7 $90.33   3.128%   $93.1555   $93.16   $93.15   $93.20  
  7 purchase totals = $821.74       $880.0799   $880.08   $880.05   $880.20