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	$244.43	4.511%	$255.4562	$255.46	$255.45	$255.50
Purchase #2	$138.86	7.166%	$148.8107	$148.81	$148.80	$148.80
Purchase #3	$51.53	5.838%	$54.5383	$54.54	$54.55	$54.50
Purchase #4	$17.45	7.386%	$18.7389	$18.74	$18.75	$18.70
Purchase #5	$26.36	11.294%	$29.3371	$29.34	$29.35	$29.30
Purchase #6	$200.68	6.751%	$214.2279	$214.23	$214.25	$214.20
Purchase #7	$248.39	3.660%	$257.4811	$257.48	$257.50	$257.50
7 purchase totals =	$927.70		$978.5902	$978.60	$978.65	$978.50