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	$122.68	9.466%	$134.2929	$134.29	$134.30	$134.30
Purchase #2	$57.75	13.201%	$65.3736	$65.37	$65.35	$65.40
Purchase #3	$171.98	7.874%	$185.5217	$185.52	$185.50	$185.50
Purchase #4	$110.78	12.470%	$124.5943	$124.59	$124.60	$124.60
Purchase #5	$185.41	13.337%	$210.1381	$210.14	$210.15	$210.10
Purchase #6	$210.54	13.363%	$238.6745	$238.67	$238.65	$238.70
Purchase #7	$109.82	9.225%	$119.9509	$119.95	$119.95	$120.00
7 purchase totals =	$968.96		$1,078.5460	$1,078.53	$1,078.50	$1,078.60