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	$141.72	9.588%	$155.3081	$155.31	$155.30	$155.30
Purchase #2	$79.27	11.341%	$88.26	$88.26	$88.25	$88.30
Purchase #3	$227.72	6.451%	$242.4102	$242.41	$242.40	$242.40
Purchase #4	$46.29	6.763%	$49.4206	$49.42	$49.40	$49.40
Purchase #5	$188.86	3.828%	$196.0896	$196.09	$196.10	$196.10
Purchase #6	$37.77	6.364%	$40.1737	$40.17	$40.15	$40.20
Purchase #7	$88.45	6.772%	$94.4398	$94.44	$94.45	$94.40
7 purchase totals =	$810.08		$866.1020	$866.10	$866.05	$866.10