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	$55.45	10.686%	$61.3754	$61.38	$61.40	$61.40
Purchase #2	$129.42	8.820%	$140.8348	$140.83	$140.85	$140.80
Purchase #3	$136.50	4.297%	$142.3654	$142.37	$142.35	$142.40
Purchase #4	$146.83	4.496%	$153.4315	$153.43	$153.45	$153.40
Purchase #5	$228.89	12.750%	$258.0735	$258.07	$258.05	$258.10
Purchase #6	$215.87	10.261%	$238.0204	$238.02	$238.00	$238.00
Purchase #7	$200.61	11.770%	$224.2218	$224.22	$224.20	$224.20
7 purchase totals =	$1,113.57		$1,218.3228	$1,218.32	$1,218.30	$1,218.30