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	$249.44	11.604%	$278.385	$278.39	$278.40	$278.40
Purchase #2	$73.94	11.505%	$82.4468	$82.45	$82.45	$82.40
Purchase #3	$13.34	12.302%	$14.9811	$14.98	$15.00	$15.00
Purchase #4	$125.76	12.429%	$141.3907	$141.39	$141.40	$141.40
Purchase #5	$36.73	12.627%	$41.3679	$41.37	$41.35	$41.40
Purchase #6	$144.42	4.522%	$150.9507	$150.95	$150.95	$151.00
Purchase #7	$233.60	13.345%	$264.7739	$264.77	$264.75	$264.80
7 purchase totals =	$877.23		$974.2961	$974.30	$974.30	$974.40