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	$80.64	10.127%	$88.8064	$88.81	$88.80	$88.80
Purchase #2	$88.84	13.861%	$101.1541	$101.15	$101.15	$101.20
Purchase #3	$189.57	3.277%	$195.7822	$195.78	$195.80	$195.80
Purchase #4	$65.98	10.342%	$72.8037	$72.80	$72.80	$72.80
Purchase #5	$159.49	7.506%	$171.4613	$171.46	$171.45	$171.50
Purchase #6	$19.31	9.521%	$21.1485	$21.15	$21.15	$21.10
Purchase #7	$123.32	3.341%	$127.4401	$127.44	$127.45	$127.40
7 purchase totals =	$727.15		$778.5963	$778.59	$778.60	$778.60