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	$14.39	7.696%	$15.4975	$15.50	$15.50	$15.50
Purchase #2	$90.96	9.166%	$99.2974	$99.30	$99.30	$99.30
Purchase #3	$149.41	12.306%	$167.7964	$167.80	$167.80	$167.80
Purchase #4	$176.74	5.731%	$186.869	$186.87	$186.85	$186.90
Purchase #5	$95.56	13.675%	$108.6278	$108.63	$108.65	$108.60
Purchase #6	$117.67	12.868%	$132.8118	$132.81	$132.80	$132.80
Purchase #7	$104.46	4.526%	$109.1879	$109.19	$109.20	$109.20
7 purchase totals =	$749.19		$820.0878	$820.10	$820.10	$820.10