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	$230.54	12.195%	$258.6544	$258.65	$258.65	$258.70
Purchase #2	$79.77	7.546%	$85.7894	$85.79	$85.80	$85.80
Purchase #3	$113.30	11.334%	$126.1414	$126.14	$126.15	$126.10
Purchase #4	$126.60	5.160%	$133.1326	$133.13	$133.15	$133.10
Purchase #5	$82.30	8.465%	$89.2667	$89.27	$89.25	$89.30
Purchase #6	$85.29	3.404%	$88.1933	$88.19	$88.20	$88.20
Purchase #7	$130.79	9.389%	$143.0699	$143.07	$143.05	$143.10
7 purchase totals =	$848.59		$924.2477	$924.24	$924.25	$924.30