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	$45.51	11.805%	$50.8825	$50.88	$50.90	$50.90
Purchase #2	$75.87	10.563%	$83.8841	$83.88	$83.90	$83.90
Purchase #3	$8.73	4.170%	$9.094	$9.09	$9.10	$9.10
Purchase #4	$216.74	6.679%	$231.2161	$231.22	$231.20	$231.20
Purchase #5	$186.81	5.353%	$196.8099	$196.81	$196.80	$196.80
Purchase #6	$114.94	11.772%	$128.4707	$128.47	$128.45	$128.50
Purchase #7	$21.78	10.685%	$24.1072	$24.11	$24.10	$24.10
7 purchase totals =	$670.38		$724.4645	$724.46	$724.45	$724.50