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	$116.77	12.705%	$131.6056	$131.61	$131.60	$131.60
Purchase #2	$150.69	12.237%	$169.1299	$169.13	$169.15	$169.10
Purchase #3	$118.34	4.286%	$123.4121	$123.41	$123.40	$123.40
Purchase #4	$96.27	8.687%	$104.633	$104.63	$104.65	$104.60
Purchase #5	$218.26	10.528%	$241.2384	$241.24	$241.25	$241.20
Purchase #6	$10.76	3.709%	$11.1591	$11.16	$11.15	$11.20
Purchase #7	$36.25	8.196%	$39.2211	$39.22	$39.20	$39.20
7 purchase totals =	$747.34		$820.3992	$820.40	$820.40	$820.30