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	$85.31	5.205%	$89.7504	$89.75	$89.75	$89.80
Purchase #2	$78.46	6.196%	$83.3214	$83.32	$83.30	$83.30
Purchase #3	$204.29	4.464%	$213.4095	$213.41	$213.40	$213.40
Purchase #4	$37.52	13.697%	$42.6591	$42.66	$42.65	$42.70
Purchase #5	$29.27	12.695%	$32.9858	$32.99	$33.00	$33.00
Purchase #6	$66.38	6.286%	$70.5526	$70.55	$70.55	$70.60
Purchase #7	$71.53	5.432%	$75.4155	$75.42	$75.40	$75.40
7 purchase totals =	$572.76		$608.0943	$608.10	$608.05	$608.20