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	$51.56	9.223%	$56.3154	$56.32	$56.30	$56.30
Purchase #2	$207.45	13.795%	$236.0677	$236.07	$236.05	$236.10
Purchase #3	$180.57	3.237%	$186.4151	$186.42	$186.40	$186.40
Purchase #4	$68.39	6.388%	$72.7588	$72.76	$72.75	$72.80
Purchase #5	$151.90	3.440%	$157.1254	$157.13	$157.15	$157.10
Purchase #6	$50.82	8.551%	$55.1656	$55.17	$55.15	$55.20
Purchase #7	$78.91	13.581%	$89.6268	$89.63	$89.65	$89.60
7 purchase totals =	$789.60		$853.4748	$853.50	$853.45	$853.50