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	$124.42	3.363%	$128.6042	$128.60	$128.60	$128.60
Purchase #2	$241.30	7.473%	$259.3323	$259.33	$259.35	$259.30
Purchase #3	$119.39	3.247%	$123.2666	$123.27	$123.25	$123.30
Purchase #4	$137.50	11.577%	$153.4184	$153.42	$153.40	$153.40
Purchase #5	$246.69	12.412%	$277.3092	$277.31	$277.30	$277.30
Purchase #6	$97.90	9.602%	$107.3004	$107.30	$107.30	$107.30
Purchase #7	$6.46	12.506%	$7.2679	$7.27	$7.25	$7.30
7 purchase totals =	$973.66		$1,056.4990	$1,056.50	$1,056.45	$1,056.50