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	$150.64	5.507%	$158.9357	$158.94	$158.95	$158.90
Purchase #2	$98.57	4.557%	$103.0618	$103.06	$103.05	$103.10
Purchase #3	$199.33	4.262%	$207.8254	$207.83	$207.85	$207.80
Purchase #4	$59.82	10.846%	$66.3081	$66.31	$66.30	$66.30
Purchase #5	$150.70	10.617%	$166.6998	$166.70	$166.70	$166.70
Purchase #6	$74.69	12.189%	$83.794	$83.79	$83.80	$83.80
Purchase #7	$111.58	10.245%	$123.0114	$123.01	$123.00	$123.00
7 purchase totals =	$845.33		$909.6362	$909.64	$909.65	$909.60