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	$182.78	6.371%	$194.4249	$194.42	$194.40	$194.40
Purchase #2	$156.30	3.774%	$162.1988	$162.20	$162.20	$162.20
Purchase #3	$244.39	7.379%	$262.4235	$262.42	$262.40	$262.40
Purchase #4	$153.81	7.308%	$165.0504	$165.05	$165.05	$165.10
Purchase #5	$137.57	13.658%	$156.3593	$156.36	$156.35	$156.40
Purchase #6	$27.51	7.634%	$29.6101	$29.61	$29.60	$29.60
Purchase #7	$12.33	12.163%	$13.8297	$13.83	$13.85	$13.80
7 purchase totals =	$914.69		$983.8967	$983.89	$983.85	$983.90