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	$233.42	3.423%	$241.41	$241.41	$241.40	$241.40
Purchase #2	$245.61	6.452%	$261.4568	$261.46	$261.45	$261.50
Purchase #3	$86.52	3.756%	$89.7697	$89.77	$89.75	$89.80
Purchase #4	$180.92	4.248%	$188.6055	$188.61	$188.60	$188.60
Purchase #5	$12.83	5.588%	$13.5469	$13.55	$13.55	$13.50
Purchase #6	$135.97	4.822%	$142.5265	$142.53	$142.55	$142.50
Purchase #7	$23.44	4.176%	$24.4189	$24.42	$24.40	$24.40
7 purchase totals =	$918.71		$961.7343	$961.75	$961.70	$961.70