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	$64.25	5.532%	$67.8043	$67.80	$67.80	$67.80
Purchase #2	$71.62	6.329%	$76.1528	$76.15	$76.15	$76.20
Purchase #3	$90.90	9.745%	$99.7582	$99.76	$99.75	$99.80
Purchase #4	$128.47	11.800%	$143.6295	$143.63	$143.65	$143.60
Purchase #5	$68.25	4.299%	$71.1841	$71.18	$71.20	$71.20
Purchase #6	$17.41	8.681%	$18.9214	$18.92	$18.90	$18.90
Purchase #7	$19.25	13.657%	$21.879	$21.88	$21.90	$21.90
7 purchase totals =	$460.15		$499.3293	$499.32	$499.35	$499.40