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	$189.97	8.188%	$205.5247	$205.52	$205.50	$205.50
Purchase #2	$171.73	11.711%	$191.8413	$191.84	$191.85	$191.80
Purchase #3	$242.81	5.540%	$256.2617	$256.26	$256.25	$256.30
Purchase #4	$126.95	5.640%	$134.11	$134.11	$134.10	$134.10
Purchase #5	$116.27	9.427%	$127.2308	$127.23	$127.25	$127.20
Purchase #6	$20.32	3.308%	$20.9922	$20.99	$21.00	$21.00
Purchase #7	$14.62	5.724%	$15.4568	$15.46	$15.45	$15.50
7 purchase totals =	$882.67		$951.4175	$951.41	$951.40	$951.40