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	$78.37	5.264%	$82.4954	$82.50	$82.50	$82.50
Purchase #2	$175.98	13.518%	$199.769	$199.77	$199.75	$199.80
Purchase #3	$158.72	11.233%	$176.549	$176.55	$176.55	$176.50
Purchase #4	$149.52	10.770%	$165.6233	$165.62	$165.60	$165.60
Purchase #5	$203.83	9.157%	$222.4947	$222.49	$222.50	$222.50
Purchase #6	$99.45	7.121%	$106.5318	$106.53	$106.55	$106.50
Purchase #7	$201.78	8.838%	$219.6133	$219.61	$219.60	$219.60
7 purchase totals =	$1,067.65		$1,173.0765	$1,173.07	$1,173.05	$1,173.00