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	$229.35	8.349%	$248.4984	$248.50	$248.50	$248.50
Purchase #2	$89.69	5.714%	$94.8149	$94.81	$94.80	$94.80
Purchase #3	$129.65	11.509%	$144.5714	$144.57	$144.55	$144.60
Purchase #4	$114.67	11.711%	$128.099	$128.10	$128.10	$128.10
Purchase #5	$75.58	9.153%	$82.4978	$82.50	$82.50	$82.50
Purchase #6	$168.75	4.187%	$175.8156	$175.82	$175.80	$175.80
Purchase #7	$131.92	10.842%	$146.2228	$146.22	$146.20	$146.20
7 purchase totals =	$939.61		$1,020.5199	$1,020.52	$1,020.45	$1,020.50