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	$224.35	12.454%	$252.2905	$252.29	$252.30	$252.30
Purchase #2	$59.43	3.843%	$61.7139	$61.71	$61.70	$61.70
Purchase #3	$74.87	13.729%	$85.1489	$85.15	$85.15	$85.10
Purchase #4	$55.65	9.137%	$60.7347	$60.73	$60.75	$60.70
Purchase #5	$105.80	6.120%	$112.275	$112.28	$112.30	$112.30
Purchase #6	$18.37	10.603%	$20.3178	$20.32	$20.30	$20.30
Purchase #7	$76.83	7.825%	$82.8419	$82.84	$82.85	$82.80
7 purchase totals =	$615.30		$675.3227	$675.32	$675.35	$675.20