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	$16.75	11.148%	$18.6173	$18.62	$18.60	$18.60
Purchase #2	$91.93	6.523%	$97.9266	$97.93	$97.95	$97.90
Purchase #3	$214.30	12.593%	$241.2868	$241.29	$241.30	$241.30
Purchase #4	$42.50	9.156%	$46.3913	$46.39	$46.40	$46.40
Purchase #5	$108.46	13.798%	$123.4253	$123.43	$123.45	$123.40
Purchase #6	$164.25	13.133%	$185.821	$185.82	$185.80	$185.80
Purchase #7	$82.33	9.792%	$90.3918	$90.39	$90.40	$90.40
7 purchase totals =	$720.52		$803.8601	$803.87	$803.90	$803.80