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	$50.39	6.455%	$53.6427	$53.64	$53.65	$53.60
Purchase #2	$56.69	6.801%	$60.5455	$60.55	$60.55	$60.50
Purchase #3	$206.77	10.230%	$227.9226	$227.92	$227.90	$227.90
Purchase #4	$172.50	4.830%	$180.8318	$180.83	$180.85	$180.80
Purchase #5	$87.40	12.445%	$98.2769	$98.28	$98.30	$98.30
Purchase #6	$52.59	11.316%	$58.5411	$58.54	$58.55	$58.50
Purchase #7	$49.52	10.486%	$54.7127	$54.71	$54.70	$54.70
7 purchase totals =	$675.86		$734.4733	$734.47	$734.50	$734.30