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	$116.27	13.140%	$131.5479	$131.55	$131.55	$131.50
Purchase #2	$238.60	13.191%	$270.0737	$270.07	$270.05	$270.10
Purchase #3	$51.45	7.788%	$55.4569	$55.46	$55.45	$55.50
Purchase #4	$123.98	4.103%	$129.0669	$129.07	$129.05	$129.10
Purchase #5	$30.38	10.696%	$33.6294	$33.63	$33.65	$33.60
Purchase #6	$244.59	13.563%	$277.7637	$277.76	$277.75	$277.80
Purchase #7	$101.74	4.168%	$105.9805	$105.98	$106.00	$106.00
7 purchase totals =	$907.01		$1,003.5190	$1,003.52	$1,003.50	$1,003.60