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	$234.54	9.108%	$255.9019	$255.90	$255.90	$255.90
Purchase #2	$210.56	4.126%	$219.2477	$219.25	$219.25	$219.20
Purchase #3	$15.29	7.534%	$16.4419	$16.44	$16.45	$16.40
Purchase #4	$11.75	4.704%	$12.3027	$12.30	$12.30	$12.30
Purchase #5	$200.83	7.712%	$216.318	$216.32	$216.30	$216.30
Purchase #6	$194.48	10.439%	$214.7818	$214.78	$214.80	$214.80
Purchase #7	$48.27	12.760%	$54.4293	$54.43	$54.45	$54.40
7 purchase totals =	$915.72		$989.4233	$989.42	$989.45	$989.30