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	$49.76	6.221%	$52.8556	$52.86	$52.85	$52.90
Purchase #2	$137.89	13.393%	$156.3576	$156.36	$156.35	$156.40
Purchase #3	$100.25	3.298%	$103.5562	$103.56	$103.55	$103.60
Purchase #4	$249.60	11.588%	$278.5236	$278.52	$278.50	$278.50
Purchase #5	$87.62	3.795%	$90.9452	$90.95	$90.95	$90.90
Purchase #6	$80.80	7.666%	$86.9941	$86.99	$87.00	$87.00
Purchase #7	$37.93	13.391%	$43.0092	$43.01	$43.00	$43.00
7 purchase totals =	$743.85		$812.2415	$812.25	$812.20	$812.30