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	$227.69	12.622%	$256.429	$256.43	$256.45	$256.40
Purchase #2	$22.66	4.396%	$23.6561	$23.66	$23.65	$23.70
Purchase #3	$49.90	5.515%	$52.652	$52.65	$52.65	$52.70
Purchase #4	$80.76	5.407%	$85.1267	$85.13	$85.15	$85.10
Purchase #5	$56.53	9.302%	$61.7884	$61.79	$61.80	$61.80
Purchase #6	$9.71	6.504%	$10.3415	$10.34	$10.35	$10.30
Purchase #7	$89.41	11.794%	$99.955	$99.96	$99.95	$100.00
7 purchase totals =	$536.66		$589.9487	$589.96	$590.00	$590.00