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	$106.96	4.264%	$111.5208	$111.52	$111.50	$111.50
Purchase #2	$97.28	13.644%	$110.5529	$110.55	$110.55	$110.60
Purchase #3	$107.45	10.386%	$118.6098	$118.61	$118.60	$118.60
Purchase #4	$24.48	6.873%	$26.1625	$26.16	$26.15	$26.20
Purchase #5	$9.94	12.821%	$11.2144	$11.21	$11.20	$11.20
Purchase #6	$37.74	4.396%	$39.3991	$39.40	$39.40	$39.40
Purchase #7	$128.61	8.425%	$139.4454	$139.45	$139.45	$139.40
7 purchase totals =	$512.46		$556.9049	$556.90	$556.85	$556.90