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	$30.79	11.853%	$34.4395	$34.44	$34.45	$34.40
Purchase #2	$175.57	9.279%	$191.8611	$191.86	$191.85	$191.90
Purchase #3	$156.25	6.557%	$166.4953	$166.50	$166.50	$166.50
Purchase #4	$87.92	5.571%	$92.818	$92.82	$92.80	$92.80
Purchase #5	$240.44	13.560%	$273.0437	$273.04	$273.05	$273.00
Purchase #6	$34.76	6.682%	$37.0827	$37.08	$37.10	$37.10
Purchase #7	$34.52	8.336%	$37.3976	$37.40	$37.40	$37.40
7 purchase totals =	$760.25		$833.1379	$833.14	$833.15	$833.10