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	$135.73	6.458%	$144.4954	$144.50	$144.50	$144.50
Purchase #2	$52.79	12.434%	$59.3539	$59.35	$59.35	$59.40
Purchase #3	$19.75	7.733%	$21.2773	$21.28	$21.30	$21.30
Purchase #4	$30.72	4.326%	$32.0489	$32.05	$32.05	$32.00
Purchase #5	$180.70	8.486%	$196.0342	$196.03	$196.05	$196.00
Purchase #6	$123.68	10.238%	$136.3424	$136.34	$136.35	$136.30
Purchase #7	$134.29	11.572%	$149.83	$149.83	$149.85	$149.80
7 purchase totals =	$677.66		$739.3821	$739.38	$739.45	$739.30