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	$157.72	12.113%	$176.8246	$176.82	$176.80	$176.80
Purchase #2	$244.55	9.333%	$267.3739	$267.37	$267.35	$267.40
Purchase #3	$40.70	12.131%	$45.6373	$45.64	$45.65	$45.60
Purchase #4	$122.85	6.338%	$130.6362	$130.64	$130.65	$130.60
Purchase #5	$88.47	12.559%	$99.5809	$99.58	$99.60	$99.60
Purchase #6	$48.37	6.555%	$51.5407	$51.54	$51.55	$51.50
Purchase #7	$39.80	11.418%	$44.3444	$44.34	$44.35	$44.30
7 purchase totals =	$742.46		$815.9380	$815.93	$815.95	$815.80