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	$84.27	9.570%	$92.3346	$92.33	$92.35	$92.30
Purchase #2	$174.37	12.733%	$196.5725	$196.57	$196.55	$196.60
Purchase #3	$245.52	10.229%	$270.6342	$270.63	$270.65	$270.60
Purchase #4	$129.64	5.255%	$136.4526	$136.45	$136.45	$136.50
Purchase #5	$183.67	3.343%	$189.8101	$189.81	$189.80	$189.80
Purchase #6	$46.51	7.866%	$50.1685	$50.17	$50.15	$50.20
Purchase #7	$46.85	13.339%	$53.0993	$53.10	$53.10	$53.10
7 purchase totals =	$910.83		$989.0718	$989.06	$989.05	$989.10