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	$148.49	4.860%	$155.7066	$155.71	$155.70	$155.70
Purchase #2	$205.50	10.603%	$227.2892	$227.29	$227.30	$227.30
Purchase #3	$230.35	5.186%	$242.296	$242.30	$242.30	$242.30
Purchase #4	$222.78	12.627%	$250.9104	$250.91	$250.90	$250.90
Purchase #5	$136.45	10.492%	$150.7663	$150.77	$150.75	$150.80
Purchase #6	$32.70	13.499%	$37.1142	$37.11	$37.10	$37.10
Purchase #7	$235.65	8.515%	$255.7156	$255.72	$255.70	$255.70
7 purchase totals =	$1,211.92		$1,319.7983	$1,319.81	$1,319.75	$1,319.80