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	$41.65	8.443%	$45.1665	$45.17	$45.15	$45.20
Purchase #2	$126.25	8.696%	$137.2287	$137.23	$137.25	$137.20
Purchase #3	$29.68	11.686%	$33.1484	$33.15	$33.15	$33.10
Purchase #4	$37.48	7.864%	$40.4274	$40.43	$40.45	$40.40
Purchase #5	$42.26	3.389%	$43.6922	$43.69	$43.70	$43.70
Purchase #6	$18.99	12.372%	$21.3394	$21.34	$21.35	$21.30
Purchase #7	$187.30	8.732%	$203.655	$203.66	$203.65	$203.70
7 purchase totals =	$483.61		$524.6576	$524.67	$524.70	$524.60