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	$183.67	13.835%	$209.0807	$209.08	$209.10	$209.10
Purchase #2	$197.48	8.812%	$214.8819	$214.88	$214.90	$214.90
Purchase #3	$89.66	5.188%	$94.3116	$94.31	$94.30	$94.30
Purchase #4	$44.70	11.199%	$49.706	$49.71	$49.70	$49.70
Purchase #5	$166.49	7.409%	$178.8252	$178.83	$178.85	$178.80
Purchase #6	$12.37	4.644%	$12.9445	$12.94	$12.95	$12.90
Purchase #7	$85.45	4.766%	$89.5225	$89.52	$89.50	$89.50
7 purchase totals =	$779.82		$849.2724	$849.27	$849.30	$849.20