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 $14.72   13.233%   $16.6679   $16.67   $16.65   $16.70  
  Purchase #2 $135.62   11.309%   $150.9573   $150.96   $150.95   $151.00  
  Purchase #3 $57.38   6.420%   $61.0638   $61.06   $61.05   $61.10  
  Purchase #4 $202.85   5.237%   $213.4733   $213.47   $213.45   $213.50  
  Purchase #5 $54.95   5.376%   $57.9041   $57.90   $57.90   $57.90  
  Purchase #6 $196.41   9.783%   $215.6248   $215.62   $215.60   $215.60  
  Purchase #7 $134.66   5.325%   $141.8306   $141.83   $141.85   $141.80  
  7 purchase totals = $796.59       $857.5218   $857.51   $857.45   $857.60