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	$57.63	3.196%	$59.4719	$59.47	$59.45	$59.50
Purchase #2	$216.76	11.435%	$241.5465	$241.55	$241.55	$241.50
Purchase #3	$172.58	8.707%	$187.6065	$187.61	$187.60	$187.60
Purchase #4	$16.31	13.159%	$18.4562	$18.46	$18.45	$18.50
Purchase #5	$34.35	12.324%	$38.5833	$38.58	$38.60	$38.60
Purchase #6	$199.27	7.753%	$214.7194	$214.72	$214.70	$214.70
Purchase #7	$48.79	6.534%	$51.9779	$51.98	$52.00	$52.00
7 purchase totals =	$745.69		$812.3617	$812.37	$812.35	$812.40