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	$160.58	11.554%	$179.1334	$179.13	$179.15	$179.10
Purchase #2	$47.50	3.244%	$49.0409	$49.04	$49.05	$49.00
Purchase #3	$66.39	8.576%	$72.0836	$72.08	$72.10	$72.10
Purchase #4	$86.28	4.497%	$90.16	$90.16	$90.15	$90.20
Purchase #5	$84.68	7.490%	$91.0225	$91.02	$91.00	$91.00
Purchase #6	$224.86	6.807%	$240.1662	$240.17	$240.15	$240.20
Purchase #7	$246.82	13.329%	$279.7186	$279.72	$279.70	$279.70
7 purchase totals =	$917.11		$1,001.3252	$1,001.32	$1,001.30	$1,001.30