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	$107.75	11.237%	$119.8579	$119.86	$119.85	$119.90
Purchase #2	$55.65	5.285%	$58.5911	$58.59	$58.60	$58.60
Purchase #3	$74.31	11.786%	$83.0682	$83.07	$83.05	$83.10
Purchase #4	$18.81	6.747%	$20.0791	$20.08	$20.10	$20.10
Purchase #5	$223.38	9.284%	$244.1186	$244.12	$244.10	$244.10
Purchase #6	$160.46	8.371%	$173.8921	$173.89	$173.90	$173.90
Purchase #7	$81.69	5.576%	$86.245	$86.25	$86.25	$86.20
7 purchase totals =	$722.05		$785.8520	$785.86	$785.85	$785.90