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	$14.33	6.709%	$15.2914	$15.29	$15.30	$15.30
Purchase #2	$149.56	6.472%	$159.2395	$159.24	$159.25	$159.20
Purchase #3	$179.58	5.706%	$189.8268	$189.83	$189.85	$189.80
Purchase #4	$175.98	9.152%	$192.0857	$192.09	$192.10	$192.10
Purchase #5	$148.61	6.654%	$158.4985	$158.50	$158.50	$158.50
Purchase #6	$209.39	12.771%	$236.1312	$236.13	$236.15	$236.10
Purchase #7	$180.44	8.866%	$196.4378	$196.44	$196.45	$196.40
7 purchase totals =	$1,057.89		$1,147.5109	$1,147.52	$1,147.60	$1,147.40