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	$98.67	9.604%	$108.1463	$108.15	$108.15	$108.10
Purchase #2	$111.66	3.251%	$115.2901	$115.29	$115.30	$115.30
Purchase #3	$50.76	3.446%	$52.5092	$52.51	$52.50	$52.50
Purchase #4	$143.66	6.603%	$153.1459	$153.15	$153.15	$153.10
Purchase #5	$48.28	13.168%	$54.6375	$54.64	$54.65	$54.60
Purchase #6	$19.30	6.450%	$20.5449	$20.54	$20.55	$20.50
Purchase #7	$52.57	3.299%	$54.3043	$54.30	$54.30	$54.30
7 purchase totals =	$524.90		$558.5782	$558.58	$558.60	$558.40