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	$137.38	5.166%	$144.4771	$144.48	$144.50	$144.50
Purchase #2	$156.84	8.671%	$170.4396	$170.44	$170.45	$170.40
Purchase #3	$137.40	11.189%	$152.7737	$152.77	$152.75	$152.80
Purchase #4	$140.91	10.264%	$155.373	$155.37	$155.35	$155.40
Purchase #5	$233.35	13.744%	$265.4216	$265.42	$265.40	$265.40
Purchase #6	$220.71	11.660%	$246.4448	$246.44	$246.45	$246.40
Purchase #7	$140.55	10.623%	$155.4806	$155.48	$155.50	$155.50
7 purchase totals =	$1,167.14		$1,290.4104	$1,290.40	$1,290.40	$1,290.40