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	$245.36	6.621%	$261.6053	$261.61	$261.60	$261.60
Purchase #2	$18.55	8.726%	$20.1687	$20.17	$20.15	$20.20
Purchase #3	$250.89	13.245%	$284.1204	$284.12	$284.10	$284.10
Purchase #4	$180.43	6.830%	$192.7534	$192.75	$192.75	$192.80
Purchase #5	$63.49	5.285%	$66.8454	$66.85	$66.85	$66.80
Purchase #6	$38.31	8.256%	$41.4729	$41.47	$41.45	$41.50
Purchase #7	$18.94	10.315%	$20.8937	$20.89	$20.90	$20.90
7 purchase totals =	$815.97		$887.8598	$887.86	$887.80	$887.90