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	$166.81	3.305%	$172.3231	$172.32	$172.30	$172.30
Purchase #2	$237.73	4.662%	$248.813	$248.81	$248.80	$248.80
Purchase #3	$116.76	10.717%	$129.2732	$129.27	$129.25	$129.30
Purchase #4	$192.77	3.248%	$199.0312	$199.03	$199.05	$199.00
Purchase #5	$59.31	3.379%	$61.3141	$61.31	$61.30	$61.30
Purchase #6	$177.39	4.806%	$185.9154	$185.92	$185.90	$185.90
Purchase #7	$48.65	4.223%	$50.7045	$50.70	$50.70	$50.70
7 purchase totals =	$999.42		$1,047.3745	$1,047.36	$1,047.30	$1,047.30