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	$9.37	10.202%	$10.3259	$10.33	$10.35	$10.30
Purchase #2	$81.52	6.324%	$86.6753	$86.68	$86.70	$86.70
Purchase #3	$247.91	3.580%	$256.7852	$256.79	$256.80	$256.80
Purchase #4	$78.76	5.386%	$83.002	$83.00	$83.00	$83.00
Purchase #5	$204.26	13.525%	$231.8862	$231.89	$231.90	$231.90
Purchase #6	$112.46	9.507%	$123.1516	$123.15	$123.15	$123.20
Purchase #7	$158.96	4.698%	$166.4279	$166.43	$166.45	$166.40
7 purchase totals =	$893.24		$958.2541	$958.27	$958.35	$958.30