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	$95.90	13.175%	$108.5348	$108.53	$108.55	$108.50
Purchase #2	$145.96	8.643%	$158.5753	$158.58	$158.60	$158.60
Purchase #3	$106.94	12.302%	$120.0958	$120.10	$120.10	$120.10
Purchase #4	$85.45	4.814%	$89.5636	$89.56	$89.55	$89.60
Purchase #5	$34.55	4.821%	$36.2157	$36.22	$36.20	$36.20
Purchase #6	$182.42	7.867%	$196.771	$196.77	$196.75	$196.80
Purchase #7	$108.73	10.770%	$120.4402	$120.44	$120.45	$120.40
7 purchase totals =	$759.95		$830.1964	$830.20	$830.20	$830.20