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	$57.37	12.788%	$64.7065	$64.71	$64.70	$64.70
Purchase #2	$233.86	9.213%	$255.4055	$255.41	$255.40	$255.40
Purchase #3	$177.58	8.616%	$192.8803	$192.88	$192.90	$192.90
Purchase #4	$167.28	13.843%	$190.4366	$190.44	$190.45	$190.40
Purchase #5	$123.26	7.674%	$132.719	$132.72	$132.70	$132.70
Purchase #6	$94.91	7.363%	$101.8982	$101.90	$101.90	$101.90
Purchase #7	$57.60	6.792%	$61.5122	$61.51	$61.50	$61.50
7 purchase totals =	$911.86		$999.5583	$999.57	$999.55	$999.50