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	$38.43	11.452%	$42.831	$42.83	$42.85	$42.80
Purchase #2	$226.68	10.414%	$250.2865	$250.29	$250.30	$250.30
Purchase #3	$233.47	11.557%	$260.4521	$260.45	$260.45	$260.50
Purchase #4	$231.43	11.395%	$257.8014	$257.80	$257.80	$257.80
Purchase #5	$103.92	8.300%	$112.5454	$112.55	$112.55	$112.50
Purchase #6	$13.89	4.143%	$14.4655	$14.47	$14.45	$14.50
Purchase #7	$56.36	13.580%	$64.0137	$64.01	$64.00	$64.00
7 purchase totals =	$904.18		$1,002.3956	$1,002.40	$1,002.40	$1,002.40