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	$176.77	4.374%	$184.5019	$184.50	$184.50	$184.50
Purchase #2	$63.51	6.334%	$67.5327	$67.53	$67.55	$67.50
Purchase #3	$78.93	12.367%	$88.6913	$88.69	$88.70	$88.70
Purchase #4	$30.73	13.533%	$34.8887	$34.89	$34.90	$34.90
Purchase #5	$17.67	5.263%	$18.6	$18.60	$18.60	$18.60
Purchase #6	$126.81	3.444%	$131.1773	$131.18	$131.20	$131.20
Purchase #7	$49.59	11.483%	$55.2844	$55.28	$55.30	$55.30
7 purchase totals =	$544.01		$580.6763	$580.67	$580.75	$580.70