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	$131.86	8.662%	$143.2817	$143.28	$143.30	$143.30
Purchase #2	$215.88	10.298%	$238.1113	$238.11	$238.10	$238.10
Purchase #3	$69.82	3.353%	$72.1611	$72.16	$72.15	$72.20
Purchase #4	$204.94	7.145%	$219.583	$219.58	$219.60	$219.60
Purchase #5	$156.45	5.320%	$164.7731	$164.77	$164.75	$164.80
Purchase #6	$24.27	13.233%	$27.4816	$27.48	$27.50	$27.50
Purchase #7	$12.78	6.873%	$13.6584	$13.66	$13.65	$13.70
7 purchase totals =	$816.00		$879.0502	$879.04	$879.05	$879.20