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	$219.86	12.404%	$247.1314	$247.13	$247.15	$247.10
Purchase #2	$56.59	9.433%	$61.9281	$61.93	$61.95	$61.90
Purchase #3	$116.98	5.411%	$123.3098	$123.31	$123.30	$123.30
Purchase #4	$144.71	10.714%	$160.2142	$160.21	$160.20	$160.20
Purchase #5	$29.78	8.631%	$32.3503	$32.35	$32.35	$32.40
Purchase #6	$234.53	8.867%	$255.3258	$255.33	$255.35	$255.30
Purchase #7	$6.58	13.720%	$7.4828	$7.48	$7.50	$7.50
7 purchase totals =	$809.03		$887.7424	$887.74	$887.80	$887.70