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	$127.62	12.451%	$143.51	$143.51	$143.50	$143.50
Purchase #2	$244.65	12.734%	$275.8037	$275.80	$275.80	$275.80
Purchase #3	$158.37	6.599%	$168.8208	$168.82	$168.80	$168.80
Purchase #4	$147.91	7.116%	$158.4353	$158.44	$158.45	$158.40
Purchase #5	$146.40	4.440%	$152.9002	$152.90	$152.90	$152.90
Purchase #6	$232.53	5.451%	$245.2052	$245.21	$245.20	$245.20
Purchase #7	$196.29	13.713%	$223.2072	$223.21	$223.20	$223.20
7 purchase totals =	$1,253.77		$1,367.8824	$1,367.89	$1,367.85	$1,367.80