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	$143.43	13.280%	$162.4775	$162.48	$162.50	$162.50
Purchase #2	$95.39	10.416%	$105.3258	$105.33	$105.35	$105.30
Purchase #3	$183.86	13.600%	$208.865	$208.87	$208.85	$208.90
Purchase #4	$114.32	6.735%	$122.0195	$122.02	$122.00	$122.00
Purchase #5	$86.86	4.295%	$90.5906	$90.59	$90.60	$90.60
Purchase #6	$140.99	7.681%	$151.8194	$151.82	$151.80	$151.80
Purchase #7	$45.26	10.720%	$50.1119	$50.11	$50.10	$50.10
7 purchase totals =	$810.11		$891.2097	$891.22	$891.20	$891.20