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	$10.36	4.373%	$10.813	$10.81	$10.80	$10.80
Purchase #2	$42.69	5.650%	$45.102	$45.10	$45.10	$45.10
Purchase #3	$198.72	11.445%	$221.4635	$221.46	$221.45	$221.50
Purchase #4	$70.61	9.699%	$77.4585	$77.46	$77.45	$77.50
Purchase #5	$202.30	6.300%	$215.0449	$215.04	$215.05	$215.00
Purchase #6	$48.77	7.162%	$52.2629	$52.26	$52.25	$52.30
Purchase #7	$45.39	8.767%	$49.3693	$49.37	$49.35	$49.40
7 purchase totals =	$618.84		$671.5141	$671.50	$671.45	$671.60