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	$39.94	7.633%	$42.9886	$42.99	$43.00	$43.00
Purchase #2	$53.95	6.350%	$57.3758	$57.38	$57.40	$57.40
Purchase #3	$173.57	13.156%	$196.4049	$196.40	$196.40	$196.40
Purchase #4	$194.30	5.703%	$205.3809	$205.38	$205.40	$205.40
Purchase #5	$164.68	10.274%	$181.5992	$181.60	$181.60	$181.60
Purchase #6	$179.96	4.450%	$187.9682	$187.97	$187.95	$188.00
Purchase #7	$187.74	11.802%	$209.8971	$209.90	$209.90	$209.90
7 purchase totals =	$994.14		$1,081.6147	$1,081.62	$1,081.65	$1,081.70