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	$147.70	6.182%	$156.8308	$156.83	$156.85	$156.80
Purchase #2	$217.80	12.297%	$244.5829	$244.58	$244.60	$244.60
Purchase #3	$81.97	9.619%	$89.8547	$89.85	$89.85	$89.90
Purchase #4	$231.47	4.582%	$242.076	$242.08	$242.10	$242.10
Purchase #5	$198.59	10.303%	$219.0507	$219.05	$219.05	$219.10
Purchase #6	$51.41	10.616%	$56.8677	$56.87	$56.85	$56.90
Purchase #7	$83.37	8.376%	$90.3531	$90.35	$90.35	$90.40
7 purchase totals =	$1,012.31		$1,099.6159	$1,099.61	$1,099.65	$1,099.80