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	$10.58	8.540%	$11.4835	$11.48	$11.50	$11.50
Purchase #2	$103.94	10.492%	$114.8454	$114.85	$114.85	$114.80
Purchase #3	$64.52	7.126%	$69.1177	$69.12	$69.10	$69.10
Purchase #4	$73.30	10.128%	$80.7238	$80.72	$80.70	$80.70
Purchase #5	$146.75	7.550%	$157.8296	$157.83	$157.85	$157.80
Purchase #6	$28.92	11.452%	$32.2319	$32.23	$32.25	$32.20
Purchase #7	$86.36	7.562%	$92.8905	$92.89	$92.90	$92.90
7 purchase totals =	$514.37		$559.1224	$559.12	$559.15	$559.00