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	$170.58	4.704%	$178.6041	$178.60	$178.60	$178.60
Purchase #2	$37.77	7.430%	$40.5763	$40.58	$40.60	$40.60
Purchase #3	$44.54	8.208%	$48.1958	$48.20	$48.20	$48.20
Purchase #4	$76.85	6.548%	$81.8821	$81.88	$81.90	$81.90
Purchase #5	$183.89	3.819%	$190.9128	$190.91	$190.90	$190.90
Purchase #6	$95.46	4.626%	$99.876	$99.88	$99.90	$99.90
Purchase #7	$234.84	6.398%	$249.8651	$249.87	$249.85	$249.90
7 purchase totals =	$843.93		$889.9122	$889.92	$889.95	$890.00