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	$164.43	8.231%	$177.9642	$177.96	$177.95	$178.00
Purchase #2	$92.98	10.264%	$102.5235	$102.52	$102.50	$102.50
Purchase #3	$188.89	10.434%	$208.5988	$208.60	$208.60	$208.60
Purchase #4	$208.64	12.499%	$234.7179	$234.72	$234.70	$234.70
Purchase #5	$134.83	12.655%	$151.8927	$151.89	$151.90	$151.90
Purchase #6	$188.66	10.692%	$208.8315	$208.83	$208.85	$208.80
Purchase #7	$157.66	5.139%	$165.7621	$165.76	$165.75	$165.80
7 purchase totals =	$1,136.09		$1,250.2907	$1,250.28	$1,250.25	$1,250.30