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	$160.34	7.396%	$172.1987	$172.20	$172.20	$172.20
Purchase #2	$80.85	10.829%	$89.6052	$89.61	$89.60	$89.60
Purchase #3	$123.29	11.669%	$137.6767	$137.68	$137.70	$137.70
Purchase #4	$170.72	7.295%	$183.174	$183.17	$183.15	$183.20
Purchase #5	$200.75	3.688%	$208.1537	$208.15	$208.15	$208.20
Purchase #6	$59.54	9.565%	$65.235	$65.24	$65.25	$65.20
Purchase #7	$58.95	6.152%	$62.5766	$62.58	$62.60	$62.60
7 purchase totals =	$854.44		$918.6199	$918.63	$918.65	$918.70