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	$74.59	10.560%	$82.4667	$82.47	$82.45	$82.50
Purchase #2	$132.85	6.629%	$141.6566	$141.66	$141.65	$141.70
Purchase #3	$28.87	9.772%	$31.6912	$31.69	$31.70	$31.70
Purchase #4	$71.51	3.251%	$73.8348	$73.83	$73.85	$73.80
Purchase #5	$103.43	12.796%	$116.6649	$116.66	$116.65	$116.70
Purchase #6	$39.76	9.643%	$43.5941	$43.59	$43.60	$43.60
Purchase #7	$92.34	7.584%	$99.3431	$99.34	$99.35	$99.30
7 purchase totals =	$543.35		$589.2514	$589.24	$589.25	$589.30