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	$70.66	10.586%	$78.1401	$78.14	$78.15	$78.10
Purchase #2	$92.48	5.485%	$97.5525	$97.55	$97.55	$97.60
Purchase #3	$194.73	9.162%	$212.5712	$212.57	$212.55	$212.60
Purchase #4	$124.59	10.121%	$137.1998	$137.20	$137.20	$137.20
Purchase #5	$59.59	4.286%	$62.144	$62.14	$62.15	$62.10
Purchase #6	$36.87	4.428%	$38.5026	$38.50	$38.50	$38.50
Purchase #7	$14.52	5.738%	$15.3532	$15.35	$15.35	$15.40
7 purchase totals =	$593.44		$641.4634	$641.45	$641.45	$641.50