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	$20.53	3.147%	$21.1761	$21.18	$21.20	$21.20
Purchase #2	$139.42	13.150%	$157.7537	$157.75	$157.75	$157.80
Purchase #3	$97.87	6.579%	$104.3089	$104.31	$104.30	$104.30
Purchase #4	$190.63	10.560%	$210.7605	$210.76	$210.75	$210.80
Purchase #5	$72.89	13.240%	$82.5406	$82.54	$82.55	$82.50
Purchase #6	$20.55	5.575%	$21.6957	$21.70	$21.70	$21.70
Purchase #7	$46.70	8.306%	$50.5789	$50.58	$50.60	$50.60
7 purchase totals =	$588.59		$648.8144	$648.82	$648.85	$648.90