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	$227.62	12.769%	$256.6848	$256.68	$256.70	$256.70
Purchase #2	$165.81	8.220%	$179.4396	$179.44	$179.45	$179.40
Purchase #3	$72.66	6.150%	$77.1286	$77.13	$77.15	$77.10
Purchase #4	$104.38	11.216%	$116.0873	$116.09	$116.10	$116.10
Purchase #5	$17.94	9.277%	$19.6043	$19.60	$19.60	$19.60
Purchase #6	$34.76	7.377%	$37.3242	$37.32	$37.30	$37.30
Purchase #7	$122.40	13.795%	$139.2851	$139.29	$139.30	$139.30
7 purchase totals =	$745.57		$825.5539	$825.55	$825.60	$825.50