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	$214.45	13.419%	$243.227	$243.23	$243.25	$243.20
Purchase #2	$46.40	7.383%	$49.8257	$49.83	$49.85	$49.80
Purchase #3	$243.47	4.114%	$253.4864	$253.49	$253.50	$253.50
Purchase #4	$6.85	12.135%	$7.6812	$7.68	$7.70	$7.70
Purchase #5	$205.66	8.603%	$223.3529	$223.35	$223.35	$223.40
Purchase #6	$78.88	13.307%	$89.3766	$89.38	$89.40	$89.40
Purchase #7	$41.95	10.365%	$46.2981	$46.30	$46.30	$46.30
7 purchase totals =	$837.66		$913.2479	$913.26	$913.35	$913.30