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	$52.35	4.665%	$54.7921	$54.79	$54.80	$54.80
Purchase #2	$134.98	13.216%	$152.819	$152.82	$152.80	$152.80
Purchase #3	$112.30	4.188%	$117.0031	$117.00	$117.00	$117.00
Purchase #4	$118.37	9.843%	$130.0212	$130.02	$130.00	$130.00
Purchase #5	$70.54	7.528%	$75.8503	$75.85	$75.85	$75.90
Purchase #6	$175.47	11.738%	$196.0667	$196.07	$196.05	$196.10
Purchase #7	$40.91	11.126%	$45.4616	$45.46	$45.45	$45.50
7 purchase totals =	$704.92		$772.0140	$772.01	$771.95	$772.10