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	$73.93	11.317%	$82.2967	$82.30	$82.30	$82.30
Purchase #2	$126.71	3.323%	$130.9206	$130.92	$130.90	$130.90
Purchase #3	$46.59	3.301%	$48.1279	$48.13	$48.15	$48.10
Purchase #4	$35.49	12.831%	$40.0437	$40.04	$40.05	$40.00
Purchase #5	$239.42	6.533%	$255.0613	$255.06	$255.05	$255.10
Purchase #6	$32.39	7.750%	$34.9002	$34.90	$34.90	$34.90
Purchase #7	$41.54	12.323%	$46.659	$46.66	$46.65	$46.70
7 purchase totals =	$596.07		$638.0094	$638.01	$638.00	$638.00