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	$21.86	6.768%	$23.3395	$23.34	$23.35	$23.30
Purchase #2	$186.49	10.219%	$205.5474	$205.55	$205.55	$205.50
Purchase #3	$247.89	5.737%	$262.1114	$262.11	$262.10	$262.10
Purchase #4	$191.38	12.739%	$215.7599	$215.76	$215.75	$215.80
Purchase #5	$89.39	12.412%	$100.4851	$100.49	$100.50	$100.50
Purchase #6	$71.28	7.853%	$76.8776	$76.88	$76.90	$76.90
Purchase #7	$159.77	4.704%	$167.2856	$167.29	$167.30	$167.30
7 purchase totals =	$968.06		$1,051.4065	$1,051.42	$1,051.45	$1,051.40