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	$243.44	9.399%	$266.3209	$266.32	$266.30	$266.30
Purchase #2	$64.25	6.802%	$68.6203	$68.62	$68.60	$68.60
Purchase #3	$78.43	13.391%	$88.9326	$88.93	$88.95	$88.90
Purchase #4	$133.72	13.583%	$151.8832	$151.88	$151.90	$151.90
Purchase #5	$28.89	12.115%	$32.39	$32.39	$32.40	$32.40
Purchase #6	$53.82	13.653%	$61.168	$61.17	$61.15	$61.20
Purchase #7	$59.51	6.337%	$63.2811	$63.28	$63.30	$63.30
7 purchase totals =	$662.06		$732.5961	$732.59	$732.60	$732.60