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 $114.62   10.487%   $126.6402   $126.64   $126.65   $126.60  
  Purchase #2 $166.32   11.715%   $185.8044   $185.80   $185.80   $185.80  
  Purchase #3 $54.92   3.698%   $56.9509   $56.95   $56.95   $57.00  
  Purchase #4 $187.82   11.364%   $209.1639   $209.16   $209.15   $209.20  
  Purchase #5 $51.69   8.674%   $56.1736   $56.17   $56.15   $56.20  
  Purchase #6 $28.99   12.859%   $32.7178   $32.72   $32.70   $32.70  
  Purchase #7 $73.43   3.426%   $75.9457   $75.95   $75.95   $75.90  
  7 purchase totals = $677.79       $743.3965   $743.39   $743.35   $743.40