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	$162.85	3.214%	$168.084	$168.08	$168.10	$168.10
Purchase #2	$198.70	9.786%	$218.1448	$218.14	$218.15	$218.10
Purchase #3	$162.59	5.811%	$172.0381	$172.04	$172.05	$172.00
Purchase #4	$103.88	8.489%	$112.6984	$112.70	$112.70	$112.70
Purchase #5	$162.61	6.774%	$173.6252	$173.63	$173.65	$173.60
Purchase #6	$39.59	6.271%	$42.0727	$42.07	$42.05	$42.10
Purchase #7	$74.86	11.622%	$83.5602	$83.56	$83.55	$83.60
7 purchase totals =	$905.08		$970.2234	$970.22	$970.25	$970.20