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 $184.25   10.277%   $203.1854   $203.19   $203.20   $203.20  
  Purchase #2 $126.35   8.662%   $137.2944   $137.29   $137.30   $137.30  
  Purchase #3 $119.69   10.744%   $132.5495   $132.55   $132.55   $132.50  
  Purchase #4 $77.96   5.432%   $82.1948   $82.19   $82.20   $82.20  
  Purchase #5 $101.90   13.283%   $115.4354   $115.44   $115.45   $115.40  
  Purchase #6 $50.99   10.191%   $56.1864   $56.19   $56.20   $56.20  
  Purchase #7 $175.62   5.521%   $185.316   $185.32   $185.30   $185.30  
  7 purchase totals = $836.76       $912.1619   $912.17   $912.20   $912.10