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	$16.25	13.472%	$18.4392	$18.44	$18.45	$18.40
Purchase #2	$28.70	8.250%	$31.0678	$31.07	$31.05	$31.10
Purchase #3	$31.90	12.615%	$35.9242	$35.92	$35.90	$35.90
Purchase #4	$168.77	6.535%	$179.7991	$179.80	$179.80	$179.80
Purchase #5	$84.34	6.646%	$89.9452	$89.95	$89.95	$89.90
Purchase #6	$121.71	13.393%	$138.0106	$138.01	$138.00	$138.00
Purchase #7	$42.93	5.771%	$45.4075	$45.41	$45.40	$45.40
7 purchase totals =	$494.60		$538.5936	$538.60	$538.55	$538.50