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	$116.49	9.324%	$127.3515	$127.35	$127.35	$127.40
Purchase #2	$97.54	8.571%	$105.9002	$105.90	$105.90	$105.90
Purchase #3	$42.90	12.665%	$48.3333	$48.33	$48.35	$48.30
Purchase #4	$21.81	7.294%	$23.4008	$23.40	$23.40	$23.40
Purchase #5	$111.67	9.485%	$122.2619	$122.26	$122.25	$122.30
Purchase #6	$171.75	11.344%	$191.2333	$191.23	$191.25	$191.20
Purchase #7	$82.95	9.349%	$90.705	$90.71	$90.70	$90.70
7 purchase totals =	$645.11		$709.1860	$709.18	$709.20	$709.20