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	$10.85	11.287%	$12.0746	$12.07	$12.05	$12.10
Purchase #2	$160.58	8.190%	$173.7315	$173.73	$173.75	$173.70
Purchase #3	$167.88	7.126%	$179.8431	$179.84	$179.85	$179.80
Purchase #4	$25.83	11.784%	$28.8738	$28.87	$28.85	$28.90
Purchase #5	$30.72	13.559%	$34.8853	$34.89	$34.90	$34.90
Purchase #6	$168.25	13.814%	$191.4921	$191.49	$191.50	$191.50
Purchase #7	$77.93	5.408%	$82.1445	$82.14	$82.15	$82.10
7 purchase totals =	$642.04		$703.0449	$703.03	$703.05	$703.00