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	$30.59	5.205%	$32.1822	$32.18	$32.20	$32.20
Purchase #2	$42.34	3.478%	$43.8126	$43.81	$43.80	$43.80
Purchase #3	$164.94	4.498%	$172.359	$172.36	$172.35	$172.40
Purchase #4	$112.87	11.110%	$125.4099	$125.41	$125.40	$125.40
Purchase #5	$103.99	12.295%	$116.7756	$116.78	$116.80	$116.80
Purchase #6	$5.53	4.138%	$5.7588	$5.76	$5.75	$5.80
Purchase #7	$12.30	12.433%	$13.8293	$13.83	$13.85	$13.80
7 purchase totals =	$472.56		$510.1274	$510.13	$510.15	$510.20