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	$17.37	8.202%	$18.7947	$18.79	$18.80	$18.80
Purchase #2	$141.93	13.181%	$160.6378	$160.64	$160.65	$160.60
Purchase #3	$159.56	4.852%	$167.3019	$167.30	$167.30	$167.30
Purchase #4	$64.48	8.665%	$70.0672	$70.07	$70.05	$70.10
Purchase #5	$43.94	6.662%	$46.8673	$46.87	$46.85	$46.90
Purchase #6	$104.75	6.863%	$111.939	$111.94	$111.95	$111.90
Purchase #7	$42.74	7.108%	$45.778	$45.78	$45.80	$45.80
7 purchase totals =	$574.77		$621.3859	$621.39	$621.40	$621.40