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	$124.68	9.229%	$136.1867	$136.19	$136.20	$136.20
Purchase #2	$131.44	9.762%	$144.2712	$144.27	$144.25	$144.30
Purchase #3	$138.52	13.674%	$157.4612	$157.46	$157.45	$157.50
Purchase #4	$106.68	10.832%	$118.2356	$118.24	$118.25	$118.20
Purchase #5	$145.91	12.620%	$164.3238	$164.32	$164.30	$164.30
Purchase #6	$67.45	6.202%	$71.6332	$71.63	$71.65	$71.60
Purchase #7	$123.89	11.272%	$137.8549	$137.85	$137.85	$137.90
7 purchase totals =	$838.57		$929.9666	$929.96	$929.95	$930.00