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	$139.84	13.116%	$158.1814	$158.18	$158.20	$158.20
Purchase #2	$24.35	6.562%	$25.9478	$25.95	$25.95	$25.90
Purchase #3	$239.45	10.609%	$264.8533	$264.85	$264.85	$264.90
Purchase #4	$92.89	8.520%	$100.8042	$100.80	$100.80	$100.80
Purchase #5	$82.76	12.767%	$93.326	$93.33	$93.35	$93.30
Purchase #6	$109.72	5.784%	$116.0662	$116.07	$116.05	$116.10
Purchase #7	$194.51	12.758%	$219.3256	$219.33	$219.35	$219.30
7 purchase totals =	$883.52		$978.5045	$978.51	$978.55	$978.50