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	$97.44	12.702%	$109.8168	$109.82	$109.80	$109.80
Purchase #2	$65.89	3.617%	$68.2732	$68.27	$68.25	$68.30
Purchase #3	$184.51	8.672%	$200.5107	$200.51	$200.50	$200.50
Purchase #4	$30.93	13.606%	$35.1383	$35.14	$35.15	$35.10
Purchase #5	$240.37	10.325%	$265.1882	$265.19	$265.20	$265.20
Purchase #6	$165.44	8.845%	$180.0732	$180.07	$180.05	$180.10
Purchase #7	$166.99	3.162%	$172.2702	$172.27	$172.25	$172.30
7 purchase totals =	$951.57		$1,031.2706	$1,031.27	$1,031.20	$1,031.30