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	$109.93	7.170%	$117.812	$117.81	$117.80	$117.80
Purchase #2	$125.74	13.290%	$142.4508	$142.45	$142.45	$142.50
Purchase #3	$215.45	8.399%	$233.5456	$233.55	$233.55	$233.50
Purchase #4	$109.96	11.707%	$122.833	$122.83	$122.85	$122.80
Purchase #5	$174.49	12.539%	$196.3693	$196.37	$196.35	$196.40
Purchase #6	$18.82	5.375%	$19.8316	$19.83	$19.85	$19.80
Purchase #7	$10.84	4.129%	$11.2876	$11.29	$11.30	$11.30
7 purchase totals =	$765.23		$844.1299	$844.13	$844.15	$844.10