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	$31.30	7.777%	$33.7342	$33.73	$33.75	$33.70
Purchase #2	$248.77	4.788%	$260.6811	$260.68	$260.70	$260.70
Purchase #3	$96.85	3.337%	$100.0819	$100.08	$100.10	$100.10
Purchase #4	$51.30	11.157%	$57.0235	$57.02	$57.00	$57.00
Purchase #5	$27.69	6.164%	$29.3968	$29.40	$29.40	$29.40
Purchase #6	$249.86	13.204%	$282.8515	$282.85	$282.85	$282.90
Purchase #7	$124.52	10.131%	$137.1351	$137.14	$137.15	$137.10
7 purchase totals =	$830.29		$900.9041	$900.90	$900.95	$900.90