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	$116.89	11.656%	$130.5147	$130.51	$130.50	$130.50
Purchase #2	$50.31	8.791%	$54.7328	$54.73	$54.75	$54.70
Purchase #3	$27.97	6.363%	$29.7497	$29.75	$29.75	$29.70
Purchase #4	$105.75	5.836%	$111.9216	$111.92	$111.90	$111.90
Purchase #5	$91.99	11.770%	$102.8172	$102.82	$102.80	$102.80
Purchase #6	$12.38	11.239%	$13.7714	$13.77	$13.75	$13.80
Purchase #7	$78.53	4.627%	$82.1636	$82.16	$82.15	$82.20
7 purchase totals =	$483.82		$525.6710	$525.66	$525.60	$525.60