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	$14.26	7.462%	$15.3241	$15.32	$15.30	$15.30
Purchase #2	$116.43	6.293%	$123.7569	$123.76	$123.75	$123.80
Purchase #3	$18.31	12.547%	$20.6074	$20.61	$20.60	$20.60
Purchase #4	$242.79	6.860%	$259.4454	$259.45	$259.45	$259.40
Purchase #5	$238.30	4.702%	$249.5049	$249.50	$249.50	$249.50
Purchase #6	$159.36	12.686%	$179.5764	$179.58	$179.60	$179.60
Purchase #7	$127.82	7.651%	$137.5995	$137.60	$137.60	$137.60
7 purchase totals =	$917.27		$985.8146	$985.82	$985.80	$985.80