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	$8.85	13.455%	$10.0408	$10.04	$10.05	$10.00
Purchase #2	$47.91	12.865%	$54.0736	$54.07	$54.05	$54.10
Purchase #3	$12.93	7.201%	$13.8611	$13.86	$13.85	$13.90
Purchase #4	$77.53	3.472%	$80.2218	$80.22	$80.20	$80.20
Purchase #5	$12.84	5.407%	$13.5343	$13.53	$13.55	$13.50
Purchase #6	$33.84	6.157%	$35.9235	$35.92	$35.90	$35.90
Purchase #7	$250.71	4.850%	$262.8694	$262.87	$262.85	$262.90
7 purchase totals =	$444.61		$470.5245	$470.51	$470.45	$470.50