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	$33.82	12.711%	$38.1189	$38.12	$38.10	$38.10
Purchase #2	$247.61	8.194%	$267.8992	$267.90	$267.90	$267.90
Purchase #3	$246.98	10.447%	$272.782	$272.78	$272.80	$272.80
Purchase #4	$131.66	11.553%	$146.8707	$146.87	$146.85	$146.90
Purchase #5	$45.40	4.322%	$47.3622	$47.36	$47.35	$47.40
Purchase #6	$64.83	11.610%	$72.3568	$72.36	$72.35	$72.40
Purchase #7	$117.74	8.386%	$127.6137	$127.61	$127.60	$127.60
7 purchase totals =	$888.04		$973.0035	$973.00	$972.95	$973.10