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	$73.41	6.465%	$78.156	$78.16	$78.15	$78.20
Purchase #2	$186.73	13.528%	$211.9908	$211.99	$212.00	$212.00
Purchase #3	$145.27	5.158%	$152.763	$152.76	$152.75	$152.80
Purchase #4	$52.89	12.732%	$59.624	$59.62	$59.60	$59.60
Purchase #5	$202.89	13.748%	$230.7833	$230.78	$230.80	$230.80
Purchase #6	$46.59	5.388%	$49.1003	$49.10	$49.10	$49.10
Purchase #7	$80.38	6.333%	$85.4705	$85.47	$85.45	$85.50
7 purchase totals =	$788.16		$867.8879	$867.88	$867.85	$868.00