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	$103.77	5.870%	$109.8613	$109.86	$109.85	$109.90
Purchase #2	$48.32	13.439%	$54.8137	$54.81	$54.80	$54.80
Purchase #3	$44.43	13.860%	$50.588	$50.59	$50.60	$50.60
Purchase #4	$189.41	10.628%	$209.5405	$209.54	$209.55	$209.50
Purchase #5	$109.84	4.757%	$115.0651	$115.07	$115.05	$115.10
Purchase #6	$243.51	3.677%	$252.4639	$252.46	$252.45	$252.50
Purchase #7	$133.34	10.201%	$146.942	$146.94	$146.95	$146.90
7 purchase totals =	$872.62		$939.2745	$939.27	$939.25	$939.30