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	$130.68	5.136%	$137.3917	$137.39	$137.40	$137.40
Purchase #2	$28.29	12.866%	$31.9298	$31.93	$31.95	$31.90
Purchase #3	$49.80	7.547%	$53.5584	$53.56	$53.55	$53.60
Purchase #4	$65.58	11.159%	$72.8981	$72.90	$72.90	$72.90
Purchase #5	$88.60	6.599%	$94.4467	$94.45	$94.45	$94.40
Purchase #6	$108.62	10.218%	$119.7188	$119.72	$119.70	$119.70
Purchase #7	$60.87	10.621%	$67.335	$67.34	$67.35	$67.30
7 purchase totals =	$532.44		$577.2785	$577.29	$577.30	$577.20