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	$107.84	10.219%	$118.8602	$118.86	$118.85	$118.90
Purchase #2	$50.72	13.104%	$57.3663	$57.37	$57.35	$57.40
Purchase #3	$31.82	8.553%	$34.5416	$34.54	$34.55	$34.50
Purchase #4	$35.98	8.656%	$39.0944	$39.09	$39.10	$39.10
Purchase #5	$137.28	6.402%	$146.0687	$146.07	$146.05	$146.10
Purchase #6	$77.41	10.172%	$85.2841	$85.28	$85.30	$85.30
Purchase #7	$29.45	8.476%	$31.9462	$31.95	$31.95	$31.90
7 purchase totals =	$470.50		$513.1615	$513.16	$513.15	$513.20