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	$19.81	12.846%	$22.3548	$22.35	$22.35	$22.40
Purchase #2	$128.42	13.278%	$145.4716	$145.47	$145.45	$145.50
Purchase #3	$126.70	3.704%	$131.393	$131.39	$131.40	$131.40
Purchase #4	$63.62	3.457%	$65.8193	$65.82	$65.80	$65.80
Purchase #5	$27.43	5.180%	$28.8509	$28.85	$28.85	$28.90
Purchase #6	$49.92	7.462%	$53.645	$53.65	$53.65	$53.60
Purchase #7	$78.54	5.123%	$82.5636	$82.56	$82.55	$82.60
7 purchase totals =	$494.44		$530.0982	$530.09	$530.05	$530.20