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	$9.32	7.622%	$10.0304	$10.03	$10.05	$10.00
Purchase #2	$45.47	10.285%	$50.1466	$50.15	$50.15	$50.10
Purchase #3	$128.96	3.293%	$133.2067	$133.21	$133.20	$133.20
Purchase #4	$67.31	4.287%	$70.1956	$70.20	$70.20	$70.20
Purchase #5	$122.58	4.253%	$127.7933	$127.79	$127.80	$127.80
Purchase #6	$105.45	11.785%	$117.8773	$117.88	$117.90	$117.90
Purchase #7	$40.51	11.446%	$45.1468	$45.15	$45.15	$45.10
7 purchase totals =	$519.60		$554.3967	$554.41	$554.45	$554.30