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	$27.53	3.365%	$28.4564	$28.46	$28.45	$28.50
Purchase #2	$77.72	10.577%	$85.9404	$85.94	$85.95	$85.90
Purchase #3	$213.33	12.564%	$240.1328	$240.13	$240.15	$240.10
Purchase #4	$172.67	11.222%	$192.047	$192.05	$192.05	$192.00
Purchase #5	$32.43	5.743%	$34.2925	$34.29	$34.30	$34.30
Purchase #6	$87.25	9.464%	$95.5073	$95.51	$95.50	$95.50
Purchase #7	$250.77	11.601%	$279.8618	$279.86	$279.85	$279.90
7 purchase totals =	$861.70		$956.2382	$956.24	$956.25	$956.20