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	$227.28	7.586%	$244.5215	$244.52	$244.50	$244.50
Purchase #2	$227.75	12.518%	$256.2597	$256.26	$256.25	$256.30
Purchase #3	$243.62	10.874%	$270.1112	$270.11	$270.10	$270.10
Purchase #4	$22.91	7.420%	$24.6099	$24.61	$24.60	$24.60
Purchase #5	$76.91	12.229%	$86.3153	$86.32	$86.30	$86.30
Purchase #6	$73.38	5.534%	$77.4408	$77.44	$77.45	$77.40
Purchase #7	$65.56	10.382%	$72.3664	$72.37	$72.35	$72.40
7 purchase totals =	$937.41		$1,031.6248	$1,031.63	$1,031.55	$1,031.60