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	$132.27	6.389%	$140.7207	$140.72	$140.70	$140.70
Purchase #2	$64.91	10.706%	$71.8593	$71.86	$71.85	$71.90
Purchase #3	$244.65	7.198%	$262.2599	$262.26	$262.25	$262.30
Purchase #4	$100.40	13.864%	$114.3195	$114.32	$114.30	$114.30
Purchase #5	$238.80	9.179%	$260.7195	$260.72	$260.70	$260.70
Purchase #6	$55.65	6.794%	$59.4309	$59.43	$59.45	$59.40
Purchase #7	$97.39	9.420%	$106.5641	$106.56	$106.55	$106.60
7 purchase totals =	$934.07		$1,015.8739	$1,015.87	$1,015.80	$1,015.90