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	$28.56	13.119%	$32.3068	$32.31	$32.30	$32.30
Purchase #2	$79.27	5.143%	$83.3469	$83.35	$83.35	$83.30
Purchase #3	$25.51	10.626%	$28.2207	$28.22	$28.20	$28.20
Purchase #4	$230.86	6.782%	$246.5169	$246.52	$246.50	$246.50
Purchase #5	$93.54	12.591%	$105.3176	$105.32	$105.30	$105.30
Purchase #6	$77.65	13.415%	$88.0667	$88.07	$88.05	$88.10
Purchase #7	$188.90	12.160%	$211.8702	$211.87	$211.85	$211.90
7 purchase totals =	$724.29		$795.6458	$795.66	$795.55	$795.60