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	$67.91	6.780%	$72.5143	$72.51	$72.50	$72.50
Purchase #2	$207.97	7.508%	$223.5844	$223.58	$223.60	$223.60
Purchase #3	$158.91	5.457%	$167.5817	$167.58	$167.60	$167.60
Purchase #4	$45.39	4.658%	$47.5043	$47.50	$47.50	$47.50
Purchase #5	$116.30	9.418%	$127.2531	$127.25	$127.25	$127.30
Purchase #6	$239.40	8.797%	$260.46	$260.46	$260.45	$260.50
Purchase #7	$219.38	7.852%	$236.6057	$236.61	$236.60	$236.60
7 purchase totals =	$1,055.26		$1,135.5035	$1,135.49	$1,135.50	$1,135.60