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	$24.37	9.173%	$26.6055	$26.61	$26.60	$26.60
Purchase #2	$146.48	12.685%	$165.061	$165.06	$165.05	$165.10
Purchase #3	$160.41	4.349%	$167.3862	$167.39	$167.40	$167.40
Purchase #4	$137.62	3.671%	$142.672	$142.67	$142.65	$142.70
Purchase #5	$81.69	6.333%	$86.8634	$86.86	$86.85	$86.90
Purchase #6	$197.86	12.463%	$222.5193	$222.52	$222.50	$222.50
Purchase #7	$116.40	5.413%	$122.7007	$122.70	$122.70	$122.70
7 purchase totals =	$864.83		$933.8081	$933.81	$933.75	$933.90