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	$226.72	10.266%	$249.9951	$250.00	$250.00	$250.00
Purchase #2	$54.53	9.717%	$59.8287	$59.83	$59.85	$59.80
Purchase #3	$62.67	5.528%	$66.1344	$66.13	$66.15	$66.10
Purchase #4	$32.74	7.866%	$35.3153	$35.32	$35.30	$35.30
Purchase #5	$10.99	11.270%	$12.2286	$12.23	$12.25	$12.20
Purchase #6	$249.51	12.551%	$280.826	$280.83	$280.85	$280.80
Purchase #7	$130.67	11.354%	$145.5063	$145.51	$145.50	$145.50
7 purchase totals =	$767.83		$849.8344	$849.85	$849.90	$849.70