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	$249.86	3.411%	$258.3827	$258.38	$258.40	$258.40
Purchase #2	$181.47	4.669%	$189.9428	$189.94	$189.95	$189.90
Purchase #3	$114.91	13.646%	$130.5906	$130.59	$130.60	$130.60
Purchase #4	$20.40	3.454%	$21.1046	$21.10	$21.10	$21.10
Purchase #5	$221.60	4.664%	$231.9354	$231.94	$231.95	$231.90
Purchase #6	$118.37	6.807%	$126.4274	$126.43	$126.45	$126.40
Purchase #7	$91.48	13.178%	$103.5352	$103.54	$103.55	$103.50
7 purchase totals =	$998.09		$1,061.9187	$1,061.92	$1,062.00	$1,061.80