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	$14.57	6.334%	$15.4929	$15.49	$15.50	$15.50
Purchase #2	$44.45	4.827%	$46.5956	$46.60	$46.60	$46.60
Purchase #3	$157.62	4.213%	$164.2605	$164.26	$164.25	$164.30
Purchase #4	$146.52	3.332%	$151.402	$151.40	$151.40	$151.40
Purchase #5	$144.43	12.458%	$162.4231	$162.42	$162.40	$162.40
Purchase #6	$63.94	13.130%	$72.3353	$72.34	$72.35	$72.30
Purchase #7	$46.79	13.112%	$52.9251	$52.93	$52.95	$52.90
7 purchase totals =	$618.32		$665.4345	$665.44	$665.45	$665.40