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	$96.90	12.312%	$108.8303	$108.83	$108.85	$108.80
Purchase #2	$175.99	10.744%	$194.8984	$194.90	$194.90	$194.90
Purchase #3	$84.34	9.503%	$92.3548	$92.35	$92.35	$92.40
Purchase #4	$177.66	6.158%	$188.6003	$188.60	$188.60	$188.60
Purchase #5	$86.39	4.530%	$90.3035	$90.30	$90.30	$90.30
Purchase #6	$156.71	8.263%	$169.6589	$169.66	$169.65	$169.70
Purchase #7	$141.69	12.853%	$159.9014	$159.90	$159.90	$159.90
7 purchase totals =	$919.68		$1,004.5476	$1,004.54	$1,004.55	$1,004.60