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 $141.51   11.407%   $157.652   $157.65   $157.65   $157.70  
  Purchase #2 $14.79   12.586%   $16.6515   $16.65   $16.65   $16.70  
  Purchase #3 $206.48   5.649%   $218.1441   $218.14   $218.15   $218.10  
  Purchase #4 $144.27   13.585%   $163.8691   $163.87   $163.85   $163.90  
  Purchase #5 $53.89   4.492%   $56.3107   $56.31   $56.30   $56.30  
  Purchase #6 $95.87   6.321%   $101.9299   $101.93   $101.95   $101.90  
  Purchase #7 $49.33   7.248%   $52.9054   $52.91   $52.90   $52.90  
  7 purchase totals = $706.14       $767.4627   $767.46   $767.45   $767.50