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	$98.97	13.420%	$112.2518	$112.25	$112.25	$112.30
Purchase #2	$34.46	5.698%	$36.4235	$36.42	$36.40	$36.40
Purchase #3	$47.40	5.492%	$50.0032	$50.00	$50.00	$50.00
Purchase #4	$94.35	4.366%	$98.4693	$98.47	$98.45	$98.50
Purchase #5	$97.59	8.270%	$105.6607	$105.66	$105.65	$105.70
Purchase #6	$86.59	3.141%	$89.3098	$89.31	$89.30	$89.30
Purchase #7	$137.31	12.617%	$154.6344	$154.63	$154.65	$154.60
7 purchase totals =	$596.67		$646.7527	$646.74	$646.70	$646.80