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	$138.82	12.802%	$156.5917	$156.59	$156.60	$156.60
Purchase #2	$112.52	13.724%	$127.9622	$127.96	$127.95	$128.00
Purchase #3	$142.62	4.869%	$149.5642	$149.56	$149.55	$149.60
Purchase #4	$25.81	7.745%	$27.809	$27.81	$27.80	$27.80
Purchase #5	$225.56	11.102%	$250.6017	$250.60	$250.60	$250.60
Purchase #6	$137.44	10.777%	$152.2519	$152.25	$152.25	$152.30
Purchase #7	$12.58	8.621%	$13.6645	$13.66	$13.65	$13.70
7 purchase totals =	$795.35		$878.4452	$878.43	$878.40	$878.60