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	$20.42	3.440%	$21.1224	$21.12	$21.10	$21.10
Purchase #2	$78.72	10.445%	$86.9423	$86.94	$86.95	$86.90
Purchase #3	$56.63	9.749%	$62.1509	$62.15	$62.15	$62.20
Purchase #4	$231.34	10.538%	$255.7186	$255.72	$255.70	$255.70
Purchase #5	$93.59	6.443%	$99.62	$99.62	$99.60	$99.60
Purchase #6	$101.41	5.667%	$107.1569	$107.16	$107.15	$107.20
Purchase #7	$99.70	4.269%	$103.9562	$103.96	$103.95	$104.00
7 purchase totals =	$681.81		$736.6673	$736.67	$736.60	$736.70