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	$87.57	3.263%	$90.4274	$90.43	$90.45	$90.40
Purchase #2	$181.54	9.771%	$199.2783	$199.28	$199.30	$199.30
Purchase #3	$98.83	6.139%	$104.8972	$104.90	$104.90	$104.90
Purchase #4	$73.32	12.406%	$82.4161	$82.42	$82.40	$82.40
Purchase #5	$217.83	10.773%	$241.2968	$241.30	$241.30	$241.30
Purchase #6	$95.53	6.640%	$101.8732	$101.87	$101.85	$101.90
Purchase #7	$8.77	11.275%	$9.7588	$9.76	$9.75	$9.80
7 purchase totals =	$763.39		$829.9478	$829.96	$829.95	$830.00