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	$79.27	13.873%	$90.2671	$90.27	$90.25	$90.30
Purchase #2	$143.65	3.473%	$148.639	$148.64	$148.65	$148.60
Purchase #3	$173.55	4.542%	$181.4326	$181.43	$181.45	$181.40
Purchase #4	$99.31	12.203%	$111.4288	$111.43	$111.45	$111.40
Purchase #5	$108.34	5.835%	$114.6616	$114.66	$114.65	$114.70
Purchase #6	$190.29	4.455%	$198.7674	$198.77	$198.75	$198.80
Purchase #7	$26.62	7.236%	$28.5462	$28.55	$28.55	$28.50
7 purchase totals =	$821.03		$873.7427	$873.75	$873.75	$873.70