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	$19.27	3.781%	$19.9986	$20.00	$20.00	$20.00
Purchase #2	$121.38	4.667%	$127.0448	$127.04	$127.05	$127.00
Purchase #3	$117.30	6.335%	$124.731	$124.73	$124.75	$124.70
Purchase #4	$168.77	12.823%	$190.4114	$190.41	$190.40	$190.40
Purchase #5	$167.47	13.624%	$190.2861	$190.29	$190.30	$190.30
Purchase #6	$232.63	3.235%	$240.1556	$240.16	$240.15	$240.20
Purchase #7	$52.35	10.415%	$57.8023	$57.80	$57.80	$57.80
7 purchase totals =	$879.17		$950.4298	$950.43	$950.45	$950.40