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	$231.60	13.174%	$262.111	$262.11	$262.10	$262.10
Purchase #2	$249.28	3.154%	$257.1423	$257.14	$257.15	$257.10
Purchase #3	$231.48	3.159%	$238.7925	$238.79	$238.80	$238.80
Purchase #4	$234.33	7.215%	$251.2369	$251.24	$251.25	$251.20
Purchase #5	$171.60	10.104%	$188.9385	$188.94	$188.95	$188.90
Purchase #6	$92.64	7.866%	$99.9271	$99.93	$99.95	$99.90
Purchase #7	$80.41	12.531%	$90.4862	$90.49	$90.50	$90.50
7 purchase totals =	$1,291.34		$1,388.6345	$1,388.64	$1,388.70	$1,388.50