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	$120.44	3.191%	$124.2832	$124.28	$124.30	$124.30
Purchase #2	$172.37	8.333%	$186.7336	$186.73	$186.75	$186.70
Purchase #3	$118.82	4.122%	$123.7178	$123.72	$123.70	$123.70
Purchase #4	$41.93	8.743%	$45.5959	$45.60	$45.60	$45.60
Purchase #5	$60.91	9.837%	$66.9017	$66.90	$66.90	$66.90
Purchase #6	$47.45	8.790%	$51.6209	$51.62	$51.60	$51.60
Purchase #7	$89.62	9.400%	$98.0443	$98.04	$98.05	$98.00
7 purchase totals =	$651.54		$696.8974	$696.89	$696.90	$696.80