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	$97.73	6.702%	$104.2799	$104.28	$104.30	$104.30
Purchase #2	$140.40	11.170%	$156.0827	$156.08	$156.10	$156.10
Purchase #3	$186.56	11.559%	$208.1245	$208.12	$208.10	$208.10
Purchase #4	$236.44	5.239%	$248.8271	$248.83	$248.85	$248.80
Purchase #5	$13.59	3.758%	$14.1007	$14.10	$14.10	$14.10
Purchase #6	$10.43	3.330%	$10.7773	$10.78	$10.80	$10.80
Purchase #7	$39.38	7.545%	$42.3512	$42.35	$42.35	$42.40
7 purchase totals =	$724.53		$784.5434	$784.54	$784.60	$784.60