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	$246.94	13.104%	$279.299	$279.30	$279.30	$279.30
Purchase #2	$221.37	12.678%	$249.4353	$249.44	$249.45	$249.40
Purchase #3	$33.76	12.408%	$37.9489	$37.95	$37.95	$37.90
Purchase #4	$141.73	3.153%	$146.1987	$146.20	$146.20	$146.20
Purchase #5	$139.31	9.534%	$152.5918	$152.59	$152.60	$152.60
Purchase #6	$151.41	5.150%	$159.2076	$159.21	$159.20	$159.20
Purchase #7	$116.27	12.123%	$130.3654	$130.37	$130.35	$130.40
7 purchase totals =	$1,050.79		$1,155.0467	$1,155.06	$1,155.05	$1,155.00