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	$173.54	4.784%	$181.8422	$181.84	$181.85	$181.80
Purchase #2	$235.61	12.424%	$264.8822	$264.88	$264.90	$264.90
Purchase #3	$82.70	9.704%	$90.7252	$90.73	$90.75	$90.70
Purchase #4	$36.56	3.863%	$37.9723	$37.97	$37.95	$38.00
Purchase #5	$54.59	9.238%	$59.633	$59.63	$59.65	$59.60
Purchase #6	$20.28	7.152%	$21.7304	$21.73	$21.75	$21.70
Purchase #7	$111.65	10.333%	$123.1868	$123.19	$123.20	$123.20
7 purchase totals =	$714.93		$779.9721	$779.97	$780.05	$779.90