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	$149.88	3.224%	$154.7121	$154.71	$154.70	$154.70
Purchase #2	$78.28	5.670%	$82.7185	$82.72	$82.70	$82.70
Purchase #3	$124.37	10.596%	$137.5482	$137.55	$137.55	$137.50
Purchase #4	$210.33	5.274%	$221.4228	$221.42	$221.40	$221.40
Purchase #5	$90.43	10.694%	$100.1006	$100.10	$100.10	$100.10
Purchase #6	$249.69	10.194%	$275.1434	$275.14	$275.15	$275.10
Purchase #7	$174.31	13.478%	$197.8035	$197.80	$197.80	$197.80
7 purchase totals =	$1,077.29		$1,169.4491	$1,169.44	$1,169.40	$1,169.30