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	$94.85	5.605%	$100.1663	$100.17	$100.15	$100.20
Purchase #2	$139.38	8.683%	$151.4824	$151.48	$151.50	$151.50
Purchase #3	$224.44	8.192%	$242.8261	$242.83	$242.85	$242.80
Purchase #4	$81.98	12.834%	$92.5013	$92.50	$92.50	$92.50
Purchase #5	$177.47	7.406%	$190.6134	$190.61	$190.60	$190.60
Purchase #6	$122.89	6.808%	$131.2564	$131.26	$131.25	$131.30
Purchase #7	$102.38	7.694%	$110.2571	$110.26	$110.25	$110.30
7 purchase totals =	$943.39		$1,019.1030	$1,019.11	$1,019.10	$1,019.20