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	$43.40	5.209%	$45.6607	$45.66	$45.65	$45.70
Purchase #2	$78.33	8.275%	$84.8118	$84.81	$84.80	$84.80
Purchase #3	$219.33	8.726%	$238.4687	$238.47	$238.45	$238.50
Purchase #4	$164.85	4.671%	$172.5501	$172.55	$172.55	$172.60
Purchase #5	$230.85	13.779%	$262.6588	$262.66	$262.65	$262.70
Purchase #6	$81.37	10.252%	$89.7121	$89.71	$89.70	$89.70
Purchase #7	$77.76	10.721%	$86.0966	$86.10	$86.10	$86.10
7 purchase totals =	$895.89		$979.9588	$979.96	$979.90	$980.10