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	$49.71	3.359%	$51.3798	$51.38	$51.40	$51.40
Purchase #2	$108.78	7.325%	$116.7481	$116.75	$116.75	$116.70
Purchase #3	$241.82	3.444%	$250.1483	$250.15	$250.15	$250.10
Purchase #4	$33.61	11.366%	$37.4301	$37.43	$37.45	$37.40
Purchase #5	$111.58	5.404%	$117.6098	$117.61	$117.60	$117.60
Purchase #6	$115.46	3.772%	$119.8152	$119.82	$119.80	$119.80
Purchase #7	$18.46	8.229%	$19.9791	$19.98	$20.00	$20.00
7 purchase totals =	$679.42		$713.1104	$713.12	$713.15	$713.00