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	$209.40	6.239%	$222.4645	$222.46	$222.45	$222.50
Purchase #2	$170.51	8.873%	$185.6394	$185.64	$185.65	$185.60
Purchase #3	$245.83	11.163%	$273.272	$273.27	$273.25	$273.30
Purchase #4	$214.91	7.407%	$230.8284	$230.83	$230.85	$230.80
Purchase #5	$146.35	7.801%	$157.7668	$157.77	$157.75	$157.80
Purchase #6	$56.75	13.723%	$64.5378	$64.54	$64.55	$64.50
Purchase #7	$143.70	13.241%	$162.7273	$162.73	$162.75	$162.70
7 purchase totals =	$1,187.45		$1,297.2362	$1,297.24	$1,297.25	$1,297.20