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	$176.58	5.433%	$186.1736	$186.17	$186.15	$186.20
Purchase #2	$230.70	10.799%	$255.6133	$255.61	$255.60	$255.60
Purchase #3	$70.61	13.622%	$80.2285	$80.23	$80.25	$80.20
Purchase #4	$159.34	5.791%	$168.5674	$168.57	$168.55	$168.60
Purchase #5	$17.93	12.221%	$20.1212	$20.12	$20.10	$20.10
Purchase #6	$81.53	10.129%	$89.7882	$89.79	$89.80	$89.80
Purchase #7	$19.63	5.745%	$20.7577	$20.76	$20.75	$20.80
7 purchase totals =	$756.32		$821.2499	$821.25	$821.20	$821.30