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	$180.90	13.428%	$205.1913	$205.19	$205.20	$205.20
Purchase #2	$156.40	9.846%	$171.7991	$171.80	$171.80	$171.80
Purchase #3	$235.57	10.324%	$259.8902	$259.89	$259.90	$259.90
Purchase #4	$113.26	12.396%	$127.2997	$127.30	$127.30	$127.30
Purchase #5	$99.54	3.596%	$103.1195	$103.12	$103.10	$103.10
Purchase #6	$134.93	9.727%	$148.0546	$148.05	$148.05	$148.10
Purchase #7	$134.91	6.379%	$143.5159	$143.52	$143.50	$143.50
7 purchase totals =	$1,055.51		$1,158.8703	$1,158.87	$1,158.85	$1,158.90