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	$59.27	10.251%	$65.3458	$65.35	$65.35	$65.30
Purchase #2	$189.45	4.840%	$198.6194	$198.62	$198.60	$198.60
Purchase #3	$132.38	6.820%	$141.4083	$141.41	$141.40	$141.40
Purchase #4	$36.33	12.477%	$40.8629	$40.86	$40.85	$40.90
Purchase #5	$194.35	13.147%	$219.9012	$219.90	$219.90	$219.90
Purchase #6	$165.49	4.560%	$173.0363	$173.04	$173.05	$173.00
Purchase #7	$40.77	12.490%	$45.8622	$45.86	$45.85	$45.90
7 purchase totals =	$818.04		$885.0361	$885.04	$885.00	$885.00