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	$22.96	11.130%	$25.5154	$25.52	$25.50	$25.50
Purchase #2	$112.42	5.332%	$118.4142	$118.41	$118.40	$118.40
Purchase #3	$41.59	4.419%	$43.4279	$43.43	$43.45	$43.40
Purchase #4	$61.89	3.269%	$63.9132	$63.91	$63.90	$63.90
Purchase #5	$125.52	10.846%	$139.1339	$139.13	$139.15	$139.10
Purchase #6	$27.51	7.610%	$29.6035	$29.60	$29.60	$29.60
Purchase #7	$81.54	8.398%	$88.3877	$88.39	$88.40	$88.40
7 purchase totals =	$473.43		$508.3958	$508.39	$508.40	$508.30