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	$147.80	3.386%	$152.8045	$152.80	$152.80	$152.80
Purchase #2	$243.43	5.306%	$256.3464	$256.35	$256.35	$256.30
Purchase #3	$150.70	11.810%	$168.4977	$168.50	$168.50	$168.50
Purchase #4	$107.91	9.842%	$118.5305	$118.53	$118.55	$118.50
Purchase #5	$58.66	13.559%	$66.6137	$66.61	$66.60	$66.60
Purchase #6	$85.58	6.654%	$91.2745	$91.27	$91.25	$91.30
Purchase #7	$34.51	13.771%	$39.2624	$39.26	$39.25	$39.30
7 purchase totals =	$828.59		$893.3297	$893.32	$893.30	$893.30