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	$33.79	10.454%	$37.3224	$37.32	$37.30	$37.30
Purchase #2	$38.78	13.278%	$43.9292	$43.93	$43.95	$43.90
Purchase #3	$146.54	7.291%	$157.2242	$157.22	$157.20	$157.20
Purchase #4	$29.92	12.622%	$33.6965	$33.70	$33.70	$33.70
Purchase #5	$138.75	12.177%	$155.6456	$155.65	$155.65	$155.60
Purchase #6	$53.40	3.106%	$55.0586	$55.06	$55.05	$55.10
Purchase #7	$98.93	6.869%	$105.7255	$105.73	$105.75	$105.70
7 purchase totals =	$540.11		$588.6020	$588.61	$588.60	$588.50