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	$34.52	11.392%	$38.4525	$38.45	$38.45	$38.50
Purchase #2	$173.81	13.187%	$196.7303	$196.73	$196.75	$196.70
Purchase #3	$66.68	6.425%	$70.9642	$70.96	$70.95	$71.00
Purchase #4	$54.56	11.830%	$61.0144	$61.01	$61.00	$61.00
Purchase #5	$218.95	6.762%	$233.7554	$233.76	$233.75	$233.80
Purchase #6	$95.57	8.660%	$103.8464	$103.85	$103.85	$103.80
Purchase #7	$175.85	13.310%	$199.2556	$199.26	$199.25	$199.30
7 purchase totals =	$819.94		$904.0188	$904.02	$904.00	$904.10