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	$5.56	4.450%	$5.8074	$5.81	$5.80	$5.80
Purchase #2	$114.75	11.351%	$127.7753	$127.78	$127.80	$127.80
Purchase #3	$31.89	12.283%	$35.807	$35.81	$35.80	$35.80
Purchase #4	$129.38	5.154%	$136.0482	$136.05	$136.05	$136.00
Purchase #5	$88.29	7.662%	$95.0548	$95.05	$95.05	$95.10
Purchase #6	$100.52	7.809%	$108.3696	$108.37	$108.35	$108.40
Purchase #7	$82.84	3.212%	$85.5008	$85.50	$85.50	$85.50
7 purchase totals =	$553.23		$594.3631	$594.37	$594.35	$594.40