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	$233.33	9.462%	$255.4077	$255.41	$255.40	$255.40
Purchase #2	$187.74	6.421%	$199.7948	$199.79	$199.80	$199.80
Purchase #3	$113.53	3.162%	$117.1198	$117.12	$117.10	$117.10
Purchase #4	$52.96	12.321%	$59.4852	$59.49	$59.50	$59.50
Purchase #5	$188.60	11.397%	$210.0947	$210.09	$210.10	$210.10
Purchase #6	$34.86	13.154%	$39.4455	$39.45	$39.45	$39.40
Purchase #7	$79.26	5.422%	$83.5575	$83.56	$83.55	$83.60
7 purchase totals =	$890.28		$964.9052	$964.91	$964.90	$964.90