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	$72.33	12.670%	$81.4942	$81.49	$81.50	$81.50
Purchase #2	$131.89	4.165%	$137.3832	$137.38	$137.40	$137.40
Purchase #3	$33.26	3.521%	$34.4311	$34.43	$34.45	$34.40
Purchase #4	$128.70	5.693%	$136.0269	$136.03	$136.05	$136.00
Purchase #5	$108.54	4.192%	$113.09	$113.09	$113.10	$113.10
Purchase #6	$201.51	4.741%	$211.0636	$211.06	$211.05	$211.10
Purchase #7	$162.92	5.773%	$172.3254	$172.33	$172.35	$172.30
7 purchase totals =	$839.15		$885.8144	$885.81	$885.90	$885.80