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	$80.39	6.630%	$85.7199	$85.72	$85.70	$85.70
Purchase #2	$166.80	7.578%	$179.4401	$179.44	$179.45	$179.40
Purchase #3	$226.92	3.380%	$234.5899	$234.59	$234.60	$234.60
Purchase #4	$81.62	11.162%	$90.7304	$90.73	$90.75	$90.70
Purchase #5	$18.27	9.330%	$19.9746	$19.97	$19.95	$20.00
Purchase #6	$66.54	7.581%	$71.5844	$71.58	$71.60	$71.60
Purchase #7	$79.40	13.726%	$90.2984	$90.30	$90.30	$90.30
7 purchase totals =	$719.94		$772.3377	$772.33	$772.35	$772.30