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	$231.92	9.784%	$254.6111	$254.61	$254.60	$254.60
Purchase #2	$165.34	4.516%	$172.8068	$172.81	$172.80	$172.80
Purchase #3	$38.63	10.340%	$42.6243	$42.62	$42.60	$42.60
Purchase #4	$173.82	3.560%	$180.008	$180.01	$180.00	$180.00
Purchase #5	$109.41	10.686%	$121.1016	$121.10	$121.10	$121.10
Purchase #6	$229.71	11.585%	$256.3219	$256.32	$256.30	$256.30
Purchase #7	$43.29	3.682%	$44.8839	$44.88	$44.90	$44.90
7 purchase totals =	$992.12		$1,072.3576	$1,072.35	$1,072.30	$1,072.30