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	$18.68	6.871%	$19.9635	$19.96	$19.95	$20.00
Purchase #2	$39.83	13.620%	$45.2548	$45.25	$45.25	$45.30
Purchase #3	$98.49	7.295%	$105.6748	$105.67	$105.65	$105.70
Purchase #4	$173.87	7.625%	$187.1276	$187.13	$187.15	$187.10
Purchase #5	$103.34	13.105%	$116.8827	$116.88	$116.90	$116.90
Purchase #6	$217.36	7.617%	$233.9163	$233.92	$233.90	$233.90
Purchase #7	$111.32	3.623%	$115.3531	$115.35	$115.35	$115.40
7 purchase totals =	$762.89		$824.1728	$824.16	$824.15	$824.30