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	$37.51	7.756%	$40.4193	$40.42	$40.40	$40.40
Purchase #2	$111.52	10.779%	$123.5407	$123.54	$123.55	$123.50
Purchase #3	$14.92	4.415%	$15.5787	$15.58	$15.60	$15.60
Purchase #4	$85.56	8.560%	$92.8839	$92.88	$92.90	$92.90
Purchase #5	$118.26	13.869%	$134.6615	$134.66	$134.65	$134.70
Purchase #6	$60.32	6.754%	$64.394	$64.39	$64.40	$64.40
Purchase #7	$60.75	4.854%	$63.6988	$63.70	$63.70	$63.70
7 purchase totals =	$488.84		$535.1769	$535.17	$535.20	$535.20