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	$29.35	13.341%	$33.2656	$33.27	$33.25	$33.30
Purchase #2	$139.87	7.715%	$150.661	$150.66	$150.65	$150.70
Purchase #3	$7.67	11.228%	$8.5312	$8.53	$8.55	$8.50
Purchase #4	$10.41	4.784%	$10.908	$10.91	$10.90	$10.90
Purchase #5	$164.48	8.577%	$178.5874	$178.59	$178.60	$178.60
Purchase #6	$236.53	4.804%	$247.8929	$247.89	$247.90	$247.90
Purchase #7	$250.68	11.851%	$280.3881	$280.39	$280.40	$280.40
7 purchase totals =	$838.99		$910.2342	$910.24	$910.25	$910.30