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	$60.32	9.253%	$65.9014	$65.90	$65.90	$65.90
Purchase #2	$118.58	13.179%	$134.2077	$134.21	$134.20	$134.20
Purchase #3	$229.98	5.176%	$241.8838	$241.88	$241.90	$241.90
Purchase #4	$104.44	11.504%	$116.4548	$116.45	$116.45	$116.50
Purchase #5	$26.96	6.659%	$28.7553	$28.76	$28.75	$28.80
Purchase #6	$214.71	13.112%	$242.8628	$242.86	$242.85	$242.90
Purchase #7	$172.78	9.833%	$189.7695	$189.77	$189.75	$189.80
7 purchase totals =	$927.77		$1,019.8353	$1,019.83	$1,019.80	$1,020.00