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	$74.65	5.785%	$78.9685	$78.97	$78.95	$79.00
Purchase #2	$17.41	7.240%	$18.6705	$18.67	$18.65	$18.70
Purchase #3	$92.73	8.366%	$100.4878	$100.49	$100.50	$100.50
Purchase #4	$204.76	4.770%	$214.5271	$214.53	$214.55	$214.50
Purchase #5	$60.85	11.547%	$67.8763	$67.88	$67.90	$67.90
Purchase #6	$45.36	10.738%	$50.2308	$50.23	$50.25	$50.20
Purchase #7	$80.44	10.114%	$88.5757	$88.58	$88.60	$88.60
7 purchase totals =	$576.20		$619.3367	$619.35	$619.40	$619.40