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 $175.27   12.244%   $196.7301   $196.73   $196.75   $196.70  
  Purchase #2 $108.85   8.253%   $117.8334   $117.83   $117.85   $117.80  
  Purchase #3 $10.85   9.131%   $11.8407   $11.84   $11.85   $11.80  
  Purchase #4 $99.98   5.776%   $105.7548   $105.75   $105.75   $105.80  
  Purchase #5 $101.60   13.422%   $115.2368   $115.24   $115.25   $115.20  
  Purchase #6 $70.75   3.161%   $72.9864   $72.99   $73.00   $73.00  
  Purchase #7 $151.83   4.710%   $158.9812   $158.98   $159.00   $159.00  
  7 purchase totals = $719.13       $779.3634   $779.36   $779.45   $779.30