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	$100.97	10.783%	$111.8576	$111.86	$111.85	$111.90
Purchase #2	$63.41	10.801%	$70.2589	$70.26	$70.25	$70.30
Purchase #3	$104.77	10.650%	$115.928	$115.93	$115.95	$115.90
Purchase #4	$39.89	5.833%	$42.2168	$42.22	$42.20	$42.20
Purchase #5	$75.92	8.617%	$82.462	$82.46	$82.45	$82.50
Purchase #6	$21.94	9.854%	$24.102	$24.10	$24.10	$24.10
Purchase #7	$92.35	11.717%	$103.1706	$103.17	$103.15	$103.20
7 purchase totals =	$499.25		$549.9959	$550.00	$549.95	$550.10