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	$22.42	10.430%	$24.7584	$24.76	$24.75	$24.80
Purchase #2	$19.72	7.582%	$21.2152	$21.22	$21.20	$21.20
Purchase #3	$134.62	10.366%	$148.5747	$148.57	$148.55	$148.60
Purchase #4	$115.91	12.390%	$130.2712	$130.27	$130.25	$130.30
Purchase #5	$18.66	7.662%	$20.0897	$20.09	$20.10	$20.10
Purchase #6	$77.47	11.644%	$86.4906	$86.49	$86.50	$86.50
Purchase #7	$200.58	10.766%	$222.1744	$222.17	$222.15	$222.20
7 purchase totals =	$589.38		$653.5742	$653.57	$653.50	$653.70