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	$104.41	10.352%	$115.2185	$115.22	$115.20	$115.20
Purchase #2	$184.38	11.804%	$206.1442	$206.14	$206.15	$206.10
Purchase #3	$12.72	5.205%	$13.3821	$13.38	$13.40	$13.40
Purchase #4	$37.68	9.481%	$41.2524	$41.25	$41.25	$41.30
Purchase #5	$22.81	12.219%	$25.5972	$25.60	$25.60	$25.60
Purchase #6	$39.32	4.599%	$41.1283	$41.13	$41.15	$41.10
Purchase #7	$147.91	7.385%	$158.8332	$158.83	$158.85	$158.80
7 purchase totals =	$549.23		$601.5559	$601.55	$601.60	$601.50