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	$75.37	4.208%	$78.5416	$78.54	$78.55	$78.50
Purchase #2	$155.85	6.805%	$166.4556	$166.46	$166.45	$166.50
Purchase #3	$53.53	4.186%	$55.7708	$55.77	$55.75	$55.80
Purchase #4	$43.31	5.111%	$45.5236	$45.52	$45.50	$45.50
Purchase #5	$196.68	10.674%	$217.6736	$217.67	$217.65	$217.70
Purchase #6	$94.91	13.367%	$107.5966	$107.60	$107.60	$107.60
Purchase #7	$218.71	8.393%	$237.0663	$237.07	$237.05	$237.10
7 purchase totals =	$838.36		$908.6281	$908.63	$908.55	$908.70