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	$53.26	4.707%	$55.7669	$55.77	$55.75	$55.80
Purchase #2	$37.62	7.656%	$40.5002	$40.50	$40.50	$40.50
Purchase #3	$160.32	8.377%	$173.75	$173.75	$173.75	$173.80
Purchase #4	$136.63	5.577%	$144.2499	$144.25	$144.25	$144.20
Purchase #5	$89.71	11.443%	$99.9755	$99.98	$100.00	$100.00
Purchase #6	$31.77	7.844%	$34.262	$34.26	$34.25	$34.30
Purchase #7	$109.82	3.652%	$113.8306	$113.83	$113.85	$113.80
7 purchase totals =	$619.13		$662.3351	$662.34	$662.35	$662.40