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	$211.61	11.340%	$235.6066	$235.61	$235.60	$235.60
Purchase #2	$175.93	8.220%	$190.3914	$190.39	$190.40	$190.40
Purchase #3	$87.95	13.311%	$99.657	$99.66	$99.65	$99.70
Purchase #4	$42.45	11.835%	$47.474	$47.47	$47.45	$47.50
Purchase #5	$138.39	10.825%	$153.3707	$153.37	$153.35	$153.40
Purchase #6	$158.74	6.124%	$168.4612	$168.46	$168.45	$168.50
Purchase #7	$82.87	3.611%	$85.8624	$85.86	$85.85	$85.90
7 purchase totals =	$897.94		$980.8233	$980.82	$980.75	$981.00