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	$239.63	6.266%	$254.6452	$254.65	$254.65	$254.60
Purchase #2	$230.25	7.591%	$247.7283	$247.73	$247.75	$247.70
Purchase #3	$40.61	4.749%	$42.5386	$42.54	$42.55	$42.50
Purchase #4	$54.27	12.301%	$60.9458	$60.95	$60.95	$60.90
Purchase #5	$224.57	7.704%	$241.8709	$241.87	$241.85	$241.90
Purchase #6	$133.81	8.225%	$144.8159	$144.82	$144.80	$144.80
Purchase #7	$79.51	7.690%	$85.6243	$85.62	$85.60	$85.60
7 purchase totals =	$1,002.65		$1,078.1690	$1,078.18	$1,078.15	$1,078.00