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	$35.38	8.387%	$38.3473	$38.35	$38.35	$38.30
Purchase #2	$155.55	8.556%	$168.8589	$168.86	$168.85	$168.90
Purchase #3	$139.84	12.325%	$157.0753	$157.08	$157.10	$157.10
Purchase #4	$45.51	3.864%	$47.2685	$47.27	$47.25	$47.30
Purchase #5	$151.80	4.163%	$158.1194	$158.12	$158.10	$158.10
Purchase #6	$60.52	11.624%	$67.5548	$67.55	$67.55	$67.60
Purchase #7	$174.64	6.425%	$185.8606	$185.86	$185.85	$185.90
7 purchase totals =	$763.24		$823.0848	$823.09	$823.05	$823.20