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 $106.89   11.603%   $119.2924   $119.29   $119.30   $119.30  
  Purchase #2 $15.47   8.262%   $16.7481   $16.75   $16.75   $16.70  
  Purchase #3 $92.92   6.622%   $99.0732   $99.07   $99.05   $99.10  
  Purchase #4 $98.92   4.788%   $103.6563   $103.66   $103.65   $103.70  
  Purchase #5 $244.83   9.343%   $267.7045   $267.70   $267.70   $267.70  
  Purchase #6 $53.62   8.560%   $58.2099   $58.21   $58.20   $58.20  
  Purchase #7 $130.57   8.489%   $141.6541   $141.65   $141.65   $141.70  
  7 purchase totals = $743.22       $806.3385   $806.33   $806.30   $806.40