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	$239.77	11.317%	$266.9048	$266.90	$266.90	$266.90
Purchase #2	$189.37	8.186%	$204.8718	$204.87	$204.85	$204.90
Purchase #3	$120.73	5.589%	$127.4776	$127.48	$127.50	$127.50
Purchase #4	$217.51	7.397%	$233.5992	$233.60	$233.60	$233.60
Purchase #5	$138.30	4.554%	$144.5982	$144.60	$144.60	$144.60
Purchase #6	$80.70	5.678%	$85.2821	$85.28	$85.30	$85.30
Purchase #7	$34.38	9.270%	$37.567	$37.57	$37.55	$37.60
7 purchase totals =	$1,020.76		$1,100.3007	$1,100.30	$1,100.30	$1,100.40