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	$86.46	7.638%	$93.0638	$93.06	$93.05	$93.10
Purchase #2	$234.31	10.389%	$258.6525	$258.65	$258.65	$258.70
Purchase #3	$53.73	10.813%	$59.5398	$59.54	$59.55	$59.50
Purchase #4	$199.42	13.455%	$226.252	$226.25	$226.25	$226.30
Purchase #5	$145.45	13.426%	$164.9781	$164.98	$165.00	$165.00
Purchase #6	$221.98	3.396%	$229.5184	$229.52	$229.50	$229.50
Purchase #7	$247.45	13.127%	$279.9328	$279.93	$279.95	$279.90
7 purchase totals =	$1,188.80		$1,311.9374	$1,311.93	$1,311.95	$1,312.00