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	$81.70	9.294%	$89.2932	$89.29	$89.30	$89.30
Purchase #2	$152.83	7.256%	$163.9193	$163.92	$163.90	$163.90
Purchase #3	$98.71	6.730%	$105.3532	$105.35	$105.35	$105.40
Purchase #4	$52.58	7.120%	$56.3237	$56.32	$56.30	$56.30
Purchase #5	$221.96	4.418%	$231.7662	$231.77	$231.75	$231.80
Purchase #6	$33.88	10.559%	$37.4574	$37.46	$37.45	$37.50
Purchase #7	$21.79	5.382%	$22.9627	$22.96	$22.95	$23.00
7 purchase totals =	$663.45		$707.0757	$707.07	$707.00	$707.20