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	$47.63	13.457%	$54.0396	$54.04	$54.05	$54.00
Purchase #2	$202.79	13.114%	$229.3839	$229.38	$229.40	$229.40
Purchase #3	$222.72	5.686%	$235.3839	$235.38	$235.40	$235.40
Purchase #4	$244.47	4.498%	$255.4663	$255.47	$255.45	$255.50
Purchase #5	$250.45	11.546%	$279.367	$279.37	$279.35	$279.40
Purchase #6	$60.33	10.134%	$66.4438	$66.44	$66.45	$66.40
Purchase #7	$194.63	13.249%	$220.4165	$220.42	$220.40	$220.40
7 purchase totals =	$1,223.02		$1,340.5010	$1,340.50	$1,340.50	$1,340.50