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	$43.46	12.613%	$48.9416	$48.94	$48.95	$48.90
Purchase #2	$54.37	13.209%	$61.5517	$61.55	$61.55	$61.60
Purchase #3	$241.48	13.840%	$274.9008	$274.90	$274.90	$274.90
Purchase #4	$133.65	5.325%	$140.7669	$140.77	$140.75	$140.80
Purchase #5	$91.94	5.143%	$96.6685	$96.67	$96.65	$96.70
Purchase #6	$215.82	8.248%	$233.6208	$233.62	$233.60	$233.60
Purchase #7	$184.89	8.528%	$200.6574	$200.66	$200.65	$200.70
7 purchase totals =	$965.61		$1,057.1077	$1,057.11	$1,057.05	$1,057.20