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	$20.53	4.537%	$21.4614	$21.46	$21.45	$21.50
Purchase #2	$123.83	11.750%	$138.38	$138.38	$138.40	$138.40
Purchase #3	$115.67	13.436%	$131.2114	$131.21	$131.20	$131.20
Purchase #4	$104.35	7.793%	$112.482	$112.48	$112.50	$112.50
Purchase #5	$153.81	5.440%	$162.1773	$162.18	$162.20	$162.20
Purchase #6	$204.31	4.630%	$213.7696	$213.77	$213.75	$213.80
Purchase #7	$34.56	4.210%	$36.015	$36.02	$36.00	$36.00
7 purchase totals =	$757.06		$815.4967	$815.50	$815.50	$815.60