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	$134.59	6.636%	$143.5214	$143.52	$143.50	$143.50
Purchase #2	$151.57	7.103%	$162.336	$162.34	$162.35	$162.30
Purchase #3	$105.62	4.331%	$110.1944	$110.19	$110.20	$110.20
Purchase #4	$36.44	11.419%	$40.6011	$40.60	$40.60	$40.60
Purchase #5	$159.49	10.665%	$176.4996	$176.50	$176.50	$176.50
Purchase #6	$160.71	5.497%	$169.5442	$169.54	$169.55	$169.50
Purchase #7	$194.73	11.175%	$216.4911	$216.49	$216.50	$216.50
7 purchase totals =	$943.15		$1,019.1878	$1,019.18	$1,019.20	$1,019.10