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 $197.93   10.269%   $218.2554   $218.26   $218.25   $218.30  
  Purchase #2 $103.49   12.547%   $116.4749   $116.47   $116.45   $116.50  
  Purchase #3 $39.27   3.608%   $40.6869   $40.69   $40.70   $40.70  
  Purchase #4 $203.83   5.325%   $214.6839   $214.68   $214.70   $214.70  
  Purchase #5 $122.62   4.246%   $127.8264   $127.83   $127.85   $127.80  
  Purchase #6 $175.42   10.443%   $193.7391   $193.74   $193.75   $193.70  
  Purchase #7 $58.26   3.152%   $60.0964   $60.10   $60.10   $60.10  
  7 purchase totals = $900.82       $971.7630   $971.77   $971.80   $971.80