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	$47.91	3.474%	$49.5744	$49.57	$49.55	$49.60
Purchase #2	$65.40	11.378%	$72.8412	$72.84	$72.85	$72.80
Purchase #3	$237.50	10.172%	$261.6585	$261.66	$261.65	$261.70
Purchase #4	$34.49	13.229%	$39.0527	$39.05	$39.05	$39.10
Purchase #5	$27.89	5.804%	$29.5087	$29.51	$29.50	$29.50
Purchase #6	$82.52	8.794%	$89.7768	$89.78	$89.80	$89.80
Purchase #7	$135.87	4.649%	$142.1866	$142.19	$142.20	$142.20
7 purchase totals =	$631.58		$684.5989	$684.60	$684.60	$684.70