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	$93.57	3.436%	$96.7851	$96.79	$96.80	$96.80
Purchase #2	$38.49	9.700%	$42.2235	$42.22	$42.20	$42.20
Purchase #3	$100.73	4.177%	$104.9375	$104.94	$104.95	$104.90
Purchase #4	$24.51	10.607%	$27.1098	$27.11	$27.10	$27.10
Purchase #5	$135.51	11.690%	$151.3511	$151.35	$151.35	$151.40
Purchase #6	$100.79	5.792%	$106.6278	$106.63	$106.65	$106.60
Purchase #7	$150.77	10.651%	$166.8285	$166.83	$166.85	$166.80
7 purchase totals =	$644.37		$695.8633	$695.87	$695.90	$695.80