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	$71.66	11.449%	$79.8644	$79.86	$79.85	$79.90
Purchase #2	$137.52	3.858%	$142.8255	$142.83	$142.85	$142.80
Purchase #3	$109.52	5.766%	$115.8349	$115.83	$115.85	$115.80
Purchase #4	$112.31	11.180%	$124.8663	$124.87	$124.85	$124.90
Purchase #5	$103.36	13.682%	$117.5017	$117.50	$117.50	$117.50
Purchase #6	$105.67	6.222%	$112.2448	$112.24	$112.25	$112.20
Purchase #7	$118.72	12.300%	$133.3226	$133.32	$133.30	$133.30
7 purchase totals =	$758.76		$826.4602	$826.45	$826.45	$826.40