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	$98.51	10.747%	$109.0969	$109.10	$109.10	$109.10
Purchase #2	$235.60	13.691%	$267.856	$267.86	$267.85	$267.90
Purchase #3	$103.55	5.267%	$109.004	$109.00	$109.00	$109.00
Purchase #4	$21.70	4.116%	$22.5932	$22.59	$22.60	$22.60
Purchase #5	$242.80	3.187%	$250.538	$250.54	$250.55	$250.50
Purchase #6	$185.42	12.787%	$209.1297	$209.13	$209.15	$209.10
Purchase #7	$200.49	5.631%	$211.7796	$211.78	$211.80	$211.80
7 purchase totals =	$1,088.07		$1,179.9974	$1,180.00	$1,180.05	$1,180.00