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	$90.35	9.207%	$98.6685	$98.67	$98.65	$98.70
Purchase #2	$134.43	12.663%	$151.4529	$151.45	$151.45	$151.50
Purchase #3	$210.37	3.413%	$217.5499	$217.55	$217.55	$217.50
Purchase #4	$189.52	3.585%	$196.3143	$196.31	$196.30	$196.30
Purchase #5	$9.98	5.119%	$10.4909	$10.49	$10.50	$10.50
Purchase #6	$92.60	10.759%	$102.5628	$102.56	$102.55	$102.60
Purchase #7	$204.52	4.675%	$214.0813	$214.08	$214.10	$214.10
7 purchase totals =	$931.77		$991.1206	$991.11	$991.10	$991.20