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	$248.48	9.789%	$272.8037	$272.80	$272.80	$272.80
Purchase #2	$45.55	13.634%	$51.7603	$51.76	$51.75	$51.80
Purchase #3	$23.38	6.432%	$24.8838	$24.88	$24.90	$24.90
Purchase #4	$94.75	9.179%	$103.4471	$103.45	$103.45	$103.40
Purchase #5	$27.74	11.786%	$31.0094	$31.01	$31.00	$31.00
Purchase #6	$154.47	11.613%	$172.4086	$172.41	$172.40	$172.40
Purchase #7	$128.59	13.303%	$145.6963	$145.70	$145.70	$145.70
7 purchase totals =	$722.96		$802.0092	$802.01	$802.00	$802.00