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	$150.73	13.283%	$170.7515	$170.75	$170.75	$170.80
Purchase #2	$34.69	9.326%	$37.9252	$37.93	$37.95	$37.90
Purchase #3	$184.50	8.869%	$200.8633	$200.86	$200.85	$200.90
Purchase #4	$18.95	11.665%	$21.1605	$21.16	$21.15	$21.20
Purchase #5	$101.99	6.340%	$108.4562	$108.46	$108.45	$108.50
Purchase #6	$244.42	5.657%	$258.2468	$258.25	$258.25	$258.20
Purchase #7	$130.75	11.103%	$145.2672	$145.27	$145.25	$145.30
7 purchase totals =	$866.03		$942.6707	$942.68	$942.65	$942.80