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	$159.83	8.171%	$172.8897	$172.89	$172.90	$172.90
Purchase #2	$190.66	6.494%	$203.0415	$203.04	$203.05	$203.00
Purchase #3	$84.93	12.587%	$95.6201	$95.62	$95.60	$95.60
Purchase #4	$231.58	4.308%	$241.5565	$241.56	$241.55	$241.60
Purchase #5	$130.68	10.128%	$143.9153	$143.92	$143.90	$143.90
Purchase #6	$165.36	12.134%	$185.4248	$185.42	$185.40	$185.40
Purchase #7	$204.50	6.829%	$218.4653	$218.47	$218.45	$218.50
7 purchase totals =	$1,167.54		$1,260.9132	$1,260.92	$1,260.85	$1,260.90