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	$56.71	5.392%	$59.7678	$59.77	$59.75	$59.80
Purchase #2	$226.25	10.724%	$250.5131	$250.51	$250.50	$250.50
Purchase #3	$18.35	8.384%	$19.8885	$19.89	$19.90	$19.90
Purchase #4	$100.39	6.872%	$107.2888	$107.29	$107.30	$107.30
Purchase #5	$181.55	7.627%	$195.3968	$195.40	$195.40	$195.40
Purchase #6	$96.93	3.767%	$100.5814	$100.58	$100.60	$100.60
Purchase #7	$59.29	11.812%	$66.2933	$66.29	$66.30	$66.30
7 purchase totals =	$739.47		$799.7297	$799.73	$799.75	$799.80