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	$11.69	11.848%	$13.075	$13.08	$13.10	$13.10
Purchase #2	$101.48	3.116%	$104.6421	$104.64	$104.65	$104.60
Purchase #3	$143.25	6.147%	$152.0556	$152.06	$152.05	$152.10
Purchase #4	$68.39	4.769%	$71.6515	$71.65	$71.65	$71.70
Purchase #5	$137.44	10.529%	$151.9111	$151.91	$151.90	$151.90
Purchase #6	$222.66	13.371%	$252.4319	$252.43	$252.45	$252.40
Purchase #7	$93.41	13.215%	$105.7541	$105.75	$105.75	$105.80
7 purchase totals =	$778.32		$851.5213	$851.52	$851.55	$851.60