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	$137.32	13.712%	$156.1493	$156.15	$156.15	$156.10
Purchase #2	$28.42	12.727%	$32.037	$32.04	$32.05	$32.00
Purchase #3	$126.88	10.160%	$139.771	$139.77	$139.75	$139.80
Purchase #4	$167.75	6.869%	$179.2727	$179.27	$179.25	$179.30
Purchase #5	$123.59	5.103%	$129.8968	$129.90	$129.90	$129.90
Purchase #6	$123.98	10.108%	$136.5119	$136.51	$136.50	$136.50
Purchase #7	$107.48	8.530%	$116.648	$116.65	$116.65	$116.60
7 purchase totals =	$815.42		$890.2867	$890.29	$890.25	$890.20