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	$135.40	5.719%	$143.1435	$143.14	$143.15	$143.10
Purchase #2	$195.59	6.489%	$208.2818	$208.28	$208.30	$208.30
Purchase #3	$90.89	9.870%	$99.8608	$99.86	$99.85	$99.90
Purchase #4	$174.76	10.302%	$192.7638	$192.76	$192.75	$192.80
Purchase #5	$133.69	8.162%	$144.6018	$144.60	$144.60	$144.60
Purchase #6	$44.95	3.397%	$46.477	$46.48	$46.50	$46.50
Purchase #7	$149.29	4.693%	$156.2962	$156.30	$156.30	$156.30
7 purchase totals =	$924.57		$991.4249	$991.42	$991.45	$991.50