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	$26.60	13.720%	$30.2495	$30.25	$30.25	$30.20
Purchase #2	$9.36	7.260%	$10.0395	$10.04	$10.05	$10.00
Purchase #3	$154.27	9.204%	$168.469	$168.47	$168.45	$168.50
Purchase #4	$83.77	6.831%	$89.4923	$89.49	$89.50	$89.50
Purchase #5	$168.51	10.512%	$186.2238	$186.22	$186.20	$186.20
Purchase #6	$149.63	6.584%	$159.4816	$159.48	$159.50	$159.50
Purchase #7	$155.25	6.698%	$165.6486	$165.65	$165.65	$165.60
7 purchase totals =	$747.39		$809.6043	$809.60	$809.60	$809.50