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	$35.32	13.339%	$40.0313	$40.03	$40.05	$40.00
Purchase #2	$146.47	12.506%	$164.7875	$164.79	$164.80	$164.80
Purchase #3	$128.94	10.457%	$142.4233	$142.42	$142.40	$142.40
Purchase #4	$72.34	5.271%	$76.153	$76.15	$76.15	$76.20
Purchase #5	$236.86	7.636%	$254.9466	$254.95	$254.95	$254.90
Purchase #6	$225.43	3.524%	$233.3742	$233.37	$233.35	$233.40
Purchase #7	$26.68	10.630%	$29.5161	$29.52	$29.50	$29.50
7 purchase totals =	$872.04		$941.2320	$941.23	$941.20	$941.20