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	$151.80	12.271%	$170.4274	$170.43	$170.45	$170.40
Purchase #2	$100.55	11.319%	$111.9313	$111.93	$111.95	$111.90
Purchase #3	$17.35	12.251%	$19.4755	$19.48	$19.50	$19.50
Purchase #4	$110.67	11.685%	$123.6018	$123.60	$123.60	$123.60
Purchase #5	$162.74	3.240%	$168.0128	$168.01	$168.00	$168.00
Purchase #6	$172.37	10.607%	$190.6533	$190.65	$190.65	$190.70
Purchase #7	$7.43	10.493%	$8.2096	$8.21	$8.20	$8.20
7 purchase totals =	$722.91		$792.3117	$792.31	$792.35	$792.30