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	$235.54	8.640%	$255.8907	$255.89	$255.90	$255.90
Purchase #2	$86.53	6.771%	$92.3889	$92.39	$92.40	$92.40
Purchase #3	$130.37	4.491%	$136.2249	$136.22	$136.20	$136.20
Purchase #4	$119.92	7.569%	$128.9967	$129.00	$129.00	$129.00
Purchase #5	$133.73	13.602%	$151.92	$151.92	$151.90	$151.90
Purchase #6	$126.28	7.790%	$136.1172	$136.12	$136.10	$136.10
Purchase #7	$33.59	12.851%	$37.9067	$37.91	$37.90	$37.90
7 purchase totals =	$865.96		$939.4451	$939.45	$939.40	$939.40