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	$240.32	13.694%	$273.2294	$273.23	$273.25	$273.20
Purchase #2	$155.43	8.372%	$168.4426	$168.44	$168.45	$168.40
Purchase #3	$169.78	10.313%	$187.2894	$187.29	$187.30	$187.30
Purchase #4	$71.64	9.385%	$78.3634	$78.36	$78.35	$78.40
Purchase #5	$220.78	8.627%	$239.8267	$239.83	$239.85	$239.80
Purchase #6	$68.30	9.247%	$74.6157	$74.62	$74.60	$74.60
Purchase #7	$29.83	5.839%	$31.5718	$31.57	$31.55	$31.60
7 purchase totals =	$956.08		$1,053.3390	$1,053.34	$1,053.35	$1,053.30