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	$74.78	10.180%	$82.3926	$82.39	$82.40	$82.40
Purchase #2	$148.77	11.241%	$165.4932	$165.49	$165.50	$165.50
Purchase #3	$152.43	13.663%	$173.2565	$173.26	$173.25	$173.30
Purchase #4	$188.25	12.282%	$211.3709	$211.37	$211.35	$211.40
Purchase #5	$138.92	9.794%	$152.5258	$152.53	$152.55	$152.50
Purchase #6	$153.77	6.342%	$163.5221	$163.52	$163.50	$163.50
Purchase #7	$48.52	4.804%	$50.8509	$50.85	$50.85	$50.90
7 purchase totals =	$905.44		$999.4120	$999.41	$999.40	$999.50