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	$37.45	13.824%	$42.6271	$42.63	$42.65	$42.60
Purchase #2	$161.32	11.841%	$180.4219	$180.42	$180.40	$180.40
Purchase #3	$199.91	13.235%	$226.3681	$226.37	$226.35	$226.40
Purchase #4	$177.53	4.483%	$185.4887	$185.49	$185.50	$185.50
Purchase #5	$30.68	10.718%	$33.9683	$33.97	$33.95	$34.00
Purchase #6	$44.52	13.404%	$50.4875	$50.49	$50.50	$50.50
Purchase #7	$130.30	13.491%	$147.8788	$147.88	$147.90	$147.90
7 purchase totals =	$781.71		$867.2404	$867.25	$867.25	$867.30