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	$224.92	6.761%	$240.1268	$240.13	$240.15	$240.10
Purchase #2	$30.47	13.742%	$34.6572	$34.66	$34.65	$34.70
Purchase #3	$81.78	9.823%	$89.8132	$89.81	$89.80	$89.80
Purchase #4	$71.77	9.388%	$78.5078	$78.51	$78.50	$78.50
Purchase #5	$130.59	13.221%	$147.8553	$147.86	$147.85	$147.90
Purchase #6	$49.89	3.835%	$51.8033	$51.80	$51.80	$51.80
Purchase #7	$137.73	5.697%	$145.5765	$145.58	$145.60	$145.60
7 purchase totals =	$727.15		$788.3401	$788.35	$788.35	$788.40