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	$221.82	8.254%	$240.129	$240.13	$240.15	$240.10
Purchase #2	$104.39	10.664%	$115.5221	$115.52	$115.50	$115.50
Purchase #3	$45.94	11.621%	$51.2787	$51.28	$51.30	$51.30
Purchase #4	$41.49	10.404%	$45.8066	$45.81	$45.80	$45.80
Purchase #5	$103.92	9.736%	$114.0377	$114.04	$114.05	$114.00
Purchase #6	$236.87	4.525%	$247.5884	$247.59	$247.60	$247.60
Purchase #7	$248.39	7.589%	$267.2403	$267.24	$267.25	$267.20
7 purchase totals =	$1,002.82		$1,081.6028	$1,081.61	$1,081.65	$1,081.50