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	$109.86	11.292%	$122.2654	$122.27	$122.25	$122.30
Purchase #2	$132.70	4.831%	$139.1107	$139.11	$139.10	$139.10
Purchase #3	$96.32	9.608%	$105.5744	$105.57	$105.55	$105.60
Purchase #4	$171.43	13.509%	$194.5885	$194.59	$194.60	$194.60
Purchase #5	$215.28	8.863%	$234.3603	$234.36	$234.35	$234.40
Purchase #6	$94.29	5.744%	$99.706	$99.71	$99.70	$99.70
Purchase #7	$209.64	12.404%	$235.6437	$235.64	$235.65	$235.60
7 purchase totals =	$1,029.52		$1,131.2490	$1,131.25	$1,131.20	$1,131.30