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	$225.35	8.676%	$244.9014	$244.90	$244.90	$244.90
Purchase #2	$99.28	4.577%	$103.824	$103.82	$103.80	$103.80
Purchase #3	$50.92	12.209%	$57.1368	$57.14	$57.15	$57.10
Purchase #4	$43.33	4.721%	$45.3756	$45.38	$45.40	$45.40
Purchase #5	$48.30	12.583%	$54.3776	$54.38	$54.40	$54.40
Purchase #6	$214.95	5.152%	$226.0242	$226.02	$226.00	$226.00
Purchase #7	$59.80	3.805%	$62.0754	$62.08	$62.10	$62.10
7 purchase totals =	$741.93		$793.7150	$793.72	$793.75	$793.70