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	$39.29	4.221%	$40.9484	$40.95	$40.95	$40.90
Purchase #2	$21.35	3.829%	$22.1675	$22.17	$22.15	$22.20
Purchase #3	$214.59	10.126%	$236.3194	$236.32	$236.30	$236.30
Purchase #4	$223.28	8.301%	$241.8145	$241.81	$241.80	$241.80
Purchase #5	$120.38	9.573%	$131.904	$131.90	$131.90	$131.90
Purchase #6	$138.38	12.466%	$155.6305	$155.63	$155.65	$155.60
Purchase #7	$142.34	5.727%	$150.4918	$150.49	$150.50	$150.50
7 purchase totals =	$899.61		$979.2761	$979.27	$979.25	$979.20