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	$62.85	5.189%	$66.1113	$66.11	$66.10	$66.10
Purchase #2	$81.57	8.434%	$88.4496	$88.45	$88.45	$88.40
Purchase #3	$199.62	11.515%	$222.6062	$222.61	$222.60	$222.60
Purchase #4	$222.29	12.680%	$250.4764	$250.48	$250.50	$250.50
Purchase #5	$60.63	13.407%	$68.7587	$68.76	$68.75	$68.80
Purchase #6	$20.43	4.454%	$21.34	$21.34	$21.35	$21.30
Purchase #7	$67.81	3.564%	$70.2267	$70.23	$70.25	$70.20
7 purchase totals =	$715.20		$787.9689	$787.98	$788.00	$787.90