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	$248.25	13.534%	$281.8482	$281.85	$281.85	$281.80
Purchase #2	$76.98	7.163%	$82.4941	$82.49	$82.50	$82.50
Purchase #3	$134.82	9.649%	$147.8288	$147.83	$147.85	$147.80
Purchase #4	$47.66	12.416%	$53.5775	$53.58	$53.60	$53.60
Purchase #5	$237.34	12.545%	$267.1143	$267.11	$267.10	$267.10
Purchase #6	$34.95	11.104%	$38.8308	$38.83	$38.85	$38.80
Purchase #7	$92.72	12.446%	$104.2599	$104.26	$104.25	$104.30
7 purchase totals =	$872.72		$975.9536	$975.95	$976.00	$975.90