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	$89.36	12.310%	$100.3602	$100.36	$100.35	$100.40
Purchase #2	$72.80	12.451%	$81.8643	$81.86	$81.85	$81.90
Purchase #3	$170.80	13.431%	$193.7401	$193.74	$193.75	$193.70
Purchase #4	$13.63	13.127%	$15.4192	$15.42	$15.40	$15.40
Purchase #5	$54.31	9.130%	$59.2685	$59.27	$59.25	$59.30
Purchase #6	$242.47	8.231%	$262.4277	$262.43	$262.45	$262.40
Purchase #7	$81.70	5.163%	$85.9182	$85.92	$85.90	$85.90
7 purchase totals =	$725.07		$798.9982	$799.00	$798.95	$799.00