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	$199.40	12.142%	$223.6111	$223.61	$223.60	$223.60
Purchase #2	$73.64	9.329%	$80.5099	$80.51	$80.50	$80.50
Purchase #3	$118.95	12.506%	$133.8259	$133.83	$133.85	$133.80
Purchase #4	$221.76	11.754%	$247.8257	$247.83	$247.85	$247.80
Purchase #5	$55.85	11.631%	$62.3459	$62.35	$62.35	$62.30
Purchase #6	$109.41	6.499%	$116.5206	$116.52	$116.50	$116.50
Purchase #7	$83.82	12.767%	$94.5213	$94.52	$94.50	$94.50
7 purchase totals =	$862.83		$959.1604	$959.17	$959.15	$959.00