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	$73.45	13.816%	$83.5979	$83.60	$83.60	$83.60
Purchase #2	$18.43	3.463%	$19.0682	$19.07	$19.05	$19.10
Purchase #3	$89.43	11.507%	$99.7207	$99.72	$99.70	$99.70
Purchase #4	$137.70	4.873%	$144.4101	$144.41	$144.40	$144.40
Purchase #5	$41.68	3.350%	$43.0763	$43.08	$43.10	$43.10
Purchase #6	$17.25	3.685%	$17.8857	$17.89	$17.90	$17.90
Purchase #7	$221.84	9.347%	$242.5754	$242.58	$242.60	$242.60
7 purchase totals =	$599.78		$650.3343	$650.35	$650.35	$650.40