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	$8.34	5.675%	$8.8133	$8.81	$8.80	$8.80
Purchase #2	$44.40	5.690%	$46.9264	$46.93	$46.95	$46.90
Purchase #3	$208.81	6.861%	$223.1365	$223.14	$223.15	$223.10
Purchase #4	$106.67	4.522%	$111.4936	$111.49	$111.50	$111.50
Purchase #5	$38.30	3.327%	$39.5742	$39.57	$39.55	$39.60
Purchase #6	$98.74	6.776%	$105.4306	$105.43	$105.45	$105.40
Purchase #7	$237.70	11.194%	$264.3081	$264.31	$264.30	$264.30
7 purchase totals =	$742.96		$799.6827	$799.68	$799.70	$799.60