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	$58.51	13.738%	$66.5481	$66.55	$66.55	$66.50
Purchase #2	$125.36	11.343%	$139.5796	$139.58	$139.60	$139.60
Purchase #3	$109.74	10.607%	$121.3801	$121.38	$121.40	$121.40
Purchase #4	$99.75	13.305%	$113.0217	$113.02	$113.00	$113.00
Purchase #5	$84.98	5.695%	$89.8196	$89.82	$89.80	$89.80
Purchase #6	$54.74	4.853%	$57.3965	$57.40	$57.40	$57.40
Purchase #7	$159.39	10.111%	$175.5059	$175.51	$175.50	$175.50
7 purchase totals =	$692.47		$763.2515	$763.26	$763.25	$763.20