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	$42.71	13.770%	$48.5912	$48.59	$48.60	$48.60
Purchase #2	$148.80	11.621%	$166.092	$166.09	$166.10	$166.10
Purchase #3	$48.91	9.809%	$53.7076	$53.71	$53.70	$53.70
Purchase #4	$240.46	3.247%	$248.2677	$248.27	$248.25	$248.30
Purchase #5	$80.63	12.422%	$90.6459	$90.65	$90.65	$90.60
Purchase #6	$49.93	7.235%	$53.5424	$53.54	$53.55	$53.50
Purchase #7	$65.29	3.275%	$67.4282	$67.43	$67.45	$67.40
7 purchase totals =	$676.73		$728.2750	$728.28	$728.30	$728.20