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	$47.69	13.315%	$54.0399	$54.04	$54.05	$54.00
Purchase #2	$245.45	12.260%	$275.5422	$275.54	$275.55	$275.50
Purchase #3	$11.57	8.248%	$12.5243	$12.52	$12.50	$12.50
Purchase #4	$51.85	3.461%	$53.6445	$53.64	$53.65	$53.60
Purchase #5	$204.28	13.156%	$231.1551	$231.16	$231.15	$231.20
Purchase #6	$155.70	9.774%	$170.9181	$170.92	$170.90	$170.90
Purchase #7	$48.25	8.821%	$52.5061	$52.51	$52.50	$52.50
7 purchase totals =	$764.79		$850.3302	$850.33	$850.30	$850.20