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	$27.49	5.135%	$28.9016	$28.90	$28.90	$28.90
Purchase #2	$144.61	6.139%	$153.4876	$153.49	$153.50	$153.50
Purchase #3	$107.90	8.211%	$116.7597	$116.76	$116.75	$116.80
Purchase #4	$250.34	8.465%	$271.5313	$271.53	$271.55	$271.50
Purchase #5	$25.72	13.296%	$29.1397	$29.14	$29.15	$29.10
Purchase #6	$138.81	4.377%	$144.8857	$144.89	$144.90	$144.90
Purchase #7	$118.47	13.227%	$134.14	$134.14	$134.15	$134.10
7 purchase totals =	$813.34		$878.8456	$878.85	$878.90	$878.80