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	$135.72	11.664%	$151.5504	$151.55	$151.55	$151.60
Purchase #2	$230.62	10.590%	$255.0427	$255.04	$255.05	$255.00
Purchase #3	$125.51	11.539%	$139.9926	$139.99	$140.00	$140.00
Purchase #4	$35.78	5.326%	$37.6856	$37.69	$37.70	$37.70
Purchase #5	$74.96	9.505%	$82.0849	$82.08	$82.10	$82.10
Purchase #6	$27.45	8.657%	$29.8263	$29.83	$29.85	$29.80
Purchase #7	$59.84	3.326%	$61.8303	$61.83	$61.85	$61.80
7 purchase totals =	$689.88		$758.0128	$758.01	$758.10	$758.00