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	$87.73	13.381%	$99.4692	$99.47	$99.45	$99.50
Purchase #2	$209.26	13.210%	$236.9032	$236.90	$236.90	$236.90
Purchase #3	$29.70	3.610%	$30.7722	$30.77	$30.75	$30.80
Purchase #4	$244.94	4.153%	$255.1124	$255.11	$255.10	$255.10
Purchase #5	$76.43	12.406%	$85.9119	$85.91	$85.90	$85.90
Purchase #6	$54.47	10.846%	$60.3778	$60.38	$60.40	$60.40
Purchase #7	$214.94	13.818%	$244.6404	$244.64	$244.65	$244.60
7 purchase totals =	$917.47		$1,013.1871	$1,013.18	$1,013.15	$1,013.20