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	$64.87	12.393%	$72.9093	$72.91	$72.90	$72.90
Purchase #2	$95.53	4.117%	$99.463	$99.46	$99.45	$99.50
Purchase #3	$60.45	4.484%	$63.1606	$63.16	$63.15	$63.20
Purchase #4	$32.44	3.182%	$33.4722	$33.47	$33.45	$33.50
Purchase #5	$69.38	12.839%	$78.2877	$78.29	$78.30	$78.30
Purchase #6	$232.66	5.169%	$244.6862	$244.69	$244.70	$244.70
Purchase #7	$241.74	3.297%	$249.7102	$249.71	$249.70	$249.70
7 purchase totals =	$797.07		$841.6892	$841.69	$841.65	$841.80