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	$100.28	5.202%	$105.4966	$105.50	$105.50	$105.50
Purchase #2	$57.86	11.489%	$64.5075	$64.51	$64.50	$64.50
Purchase #3	$38.50	6.794%	$41.1157	$41.12	$41.10	$41.10
Purchase #4	$124.76	7.461%	$134.0683	$134.07	$134.05	$134.10
Purchase #5	$119.59	5.746%	$126.4616	$126.46	$126.45	$126.50
Purchase #6	$34.72	7.306%	$37.2566	$37.26	$37.25	$37.30
Purchase #7	$90.53	12.555%	$101.896	$101.90	$101.90	$101.90
7 purchase totals =	$566.24		$610.8023	$610.82	$610.75	$610.90