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	$111.73	6.705%	$119.2215	$119.22	$119.20	$119.20
Purchase #2	$143.44	8.278%	$155.314	$155.31	$155.30	$155.30
Purchase #3	$137.46	10.788%	$152.2892	$152.29	$152.30	$152.30
Purchase #4	$87.83	6.712%	$93.7251	$93.73	$93.75	$93.70
Purchase #5	$143.29	6.242%	$152.2342	$152.23	$152.25	$152.20
Purchase #6	$51.32	4.171%	$53.4606	$53.46	$53.45	$53.50
Purchase #7	$141.71	5.308%	$149.232	$149.23	$149.25	$149.20
7 purchase totals =	$816.78		$875.4766	$875.47	$875.50	$875.40