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	$50.89	5.141%	$53.5063	$53.51	$53.50	$53.50
Purchase #2	$133.45	9.484%	$146.1064	$146.11	$146.10	$146.10
Purchase #3	$227.74	13.551%	$258.601	$258.60	$258.60	$258.60
Purchase #4	$75.59	8.212%	$81.7975	$81.80	$81.80	$81.80
Purchase #5	$197.47	13.843%	$224.8058	$224.81	$224.80	$224.80
Purchase #6	$170.72	4.604%	$178.5799	$178.58	$178.60	$178.60
Purchase #7	$54.34	9.151%	$59.3127	$59.31	$59.30	$59.30
7 purchase totals =	$910.20		$1,002.7096	$1,002.72	$1,002.70	$1,002.70