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 $58.77   12.651%   $66.205   $66.21   $66.20   $66.20  
  Purchase #2 $191.95   4.563%   $200.7087   $200.71   $200.70   $200.70  
  Purchase #3 $114.44   7.138%   $122.6087   $122.61   $122.60   $122.60  
  Purchase #4 $70.51   4.777%   $73.8783   $73.88   $73.90   $73.90  
  Purchase #5 $133.73   9.509%   $146.4464   $146.45   $146.45   $146.40  
  Purchase #6 $231.56   7.173%   $248.1698   $248.17   $248.15   $248.20  
  Purchase #7 $184.36   11.539%   $205.6333   $205.63   $205.65   $205.60  
  7 purchase totals = $985.32       $1,063.6502   $1,063.66   $1,063.65   $1,063.60