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	$10.72	10.772%	$11.8748	$11.87	$11.85	$11.90
Purchase #2	$223.60	9.261%	$244.3076	$244.31	$244.30	$244.30
Purchase #3	$250.50	7.530%	$269.3627	$269.36	$269.35	$269.40
Purchase #4	$137.96	8.834%	$150.1474	$150.15	$150.15	$150.10
Purchase #5	$112.99	9.231%	$123.4201	$123.42	$123.40	$123.40
Purchase #6	$138.65	4.190%	$144.4594	$144.46	$144.45	$144.50
Purchase #7	$89.56	10.794%	$99.2271	$99.23	$99.25	$99.20
7 purchase totals =	$963.98		$1,042.7991	$1,042.80	$1,042.75	$1,042.80