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	$133.26	5.794%	$140.9811	$140.98	$141.00	$141.00
Purchase #2	$81.90	10.660%	$90.6305	$90.63	$90.65	$90.60
Purchase #3	$68.63	8.570%	$74.5116	$74.51	$74.50	$74.50
Purchase #4	$198.74	4.722%	$208.1245	$208.12	$208.10	$208.10
Purchase #5	$241.27	12.134%	$270.5457	$270.55	$270.55	$270.50
Purchase #6	$218.50	11.850%	$244.3923	$244.39	$244.40	$244.40
Purchase #7	$95.93	4.665%	$100.4051	$100.41	$100.40	$100.40
7 purchase totals =	$1,038.23		$1,129.5908	$1,129.59	$1,129.60	$1,129.50