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	$72.29	12.465%	$81.3009	$81.30	$81.30	$81.30
Purchase #2	$104.58	6.149%	$111.0106	$111.01	$111.00	$111.00
Purchase #3	$117.61	8.660%	$127.795	$127.80	$127.80	$127.80
Purchase #4	$144.53	4.284%	$150.7217	$150.72	$150.70	$150.70
Purchase #5	$135.55	5.316%	$142.7558	$142.76	$142.75	$142.80
Purchase #6	$245.99	13.564%	$279.3561	$279.36	$279.35	$279.40
Purchase #7	$76.89	10.585%	$85.0288	$85.03	$85.05	$85.00
7 purchase totals =	$897.44		$977.9689	$977.98	$977.95	$978.00