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	$108.69	13.593%	$123.4642	$123.46	$123.45	$123.50
Purchase #2	$52.79	9.257%	$57.6768	$57.68	$57.70	$57.70
Purchase #3	$106.70	7.241%	$114.4261	$114.43	$114.45	$114.40
Purchase #4	$134.40	4.753%	$140.788	$140.79	$140.80	$140.80
Purchase #5	$35.39	13.842%	$40.2887	$40.29	$40.30	$40.30
Purchase #6	$193.92	7.405%	$208.2798	$208.28	$208.30	$208.30
Purchase #7	$13.64	13.118%	$15.4293	$15.43	$15.45	$15.40
7 purchase totals =	$645.53		$700.3529	$700.36	$700.45	$700.40