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	$39.57	8.627%	$42.9837	$42.98	$43.00	$43.00
Purchase #2	$200.42	12.521%	$225.5146	$225.51	$225.50	$225.50
Purchase #3	$153.85	10.289%	$169.6796	$169.68	$169.70	$169.70
Purchase #4	$79.66	13.376%	$90.3153	$90.32	$90.30	$90.30
Purchase #5	$177.59	4.318%	$185.2583	$185.26	$185.25	$185.30
Purchase #6	$116.95	6.470%	$124.5167	$124.52	$124.50	$124.50
Purchase #7	$63.97	12.639%	$72.0552	$72.06	$72.05	$72.10
7 purchase totals =	$832.01		$910.3234	$910.33	$910.30	$910.40