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	$175.41	4.585%	$183.4525	$183.45	$183.45	$183.50
Purchase #2	$112.61	10.741%	$124.7054	$124.71	$124.70	$124.70
Purchase #3	$59.61	11.605%	$66.5277	$66.53	$66.55	$66.50
Purchase #4	$150.73	5.173%	$158.5273	$158.53	$158.55	$158.50
Purchase #5	$86.71	13.598%	$98.5008	$98.50	$98.50	$98.50
Purchase #6	$112.53	13.485%	$127.7047	$127.70	$127.70	$127.70
Purchase #7	$40.31	9.334%	$44.0725	$44.07	$44.05	$44.10
7 purchase totals =	$737.91		$803.4909	$803.49	$803.50	$803.50