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	$29.57	13.183%	$33.4682	$33.47	$33.45	$33.50
Purchase #2	$63.67	13.870%	$72.501	$72.50	$72.50	$72.50
Purchase #3	$49.60	7.384%	$53.2625	$53.26	$53.25	$53.30
Purchase #4	$117.45	13.774%	$133.6276	$133.63	$133.65	$133.60
Purchase #5	$139.76	4.483%	$146.0254	$146.03	$146.05	$146.00
Purchase #6	$195.94	12.337%	$220.1131	$220.11	$220.10	$220.10
Purchase #7	$241.38	13.864%	$274.8449	$274.84	$274.85	$274.80
7 purchase totals =	$837.37		$933.8427	$933.84	$933.85	$933.80