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	$221.37	12.756%	$249.608	$249.61	$249.60	$249.60
Purchase #2	$98.31	11.132%	$109.2539	$109.25	$109.25	$109.30
Purchase #3	$66.65	7.371%	$71.5628	$71.56	$71.55	$71.60
Purchase #4	$211.36	6.292%	$224.6588	$224.66	$224.65	$224.70
Purchase #5	$101.50	10.786%	$112.4478	$112.45	$112.45	$112.40
Purchase #6	$230.88	13.542%	$262.1458	$262.15	$262.15	$262.10
Purchase #7	$49.65	3.679%	$51.4766	$51.48	$51.50	$51.50
7 purchase totals =	$979.72		$1,081.1537	$1,081.16	$1,081.15	$1,081.20