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	$94.39	5.183%	$99.2822	$99.28	$99.30	$99.30
Purchase #2	$178.89	12.260%	$200.8219	$200.82	$200.80	$200.80
Purchase #3	$48.90	13.239%	$55.3739	$55.37	$55.35	$55.40
Purchase #4	$51.83	3.394%	$53.5891	$53.59	$53.60	$53.60
Purchase #5	$43.79	5.639%	$46.2593	$46.26	$46.25	$46.30
Purchase #6	$84.34	7.445%	$90.6191	$90.62	$90.60	$90.60
Purchase #7	$106.58	7.104%	$114.1514	$114.15	$114.15	$114.20
7 purchase totals =	$608.72		$660.0969	$660.09	$660.05	$660.20