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	$75.42	10.806%	$83.5699	$83.57	$83.55	$83.60
Purchase #2	$96.45	7.346%	$103.5352	$103.54	$103.55	$103.50
Purchase #3	$95.88	4.443%	$100.1399	$100.14	$100.15	$100.10
Purchase #4	$189.31	13.609%	$215.0732	$215.07	$215.05	$215.10
Purchase #5	$169.48	3.829%	$175.9694	$175.97	$175.95	$176.00
Purchase #6	$32.45	9.762%	$35.6178	$35.62	$35.60	$35.60
Purchase #7	$145.99	7.380%	$156.7641	$156.76	$156.75	$156.80
7 purchase totals =	$804.98		$870.6695	$870.67	$870.60	$870.70