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	$131.92	5.694%	$139.4315	$139.43	$139.45	$139.40
Purchase #2	$103.71	9.830%	$113.9047	$113.90	$113.90	$113.90
Purchase #3	$236.84	10.751%	$262.3027	$262.30	$262.30	$262.30
Purchase #4	$191.52	8.525%	$207.8471	$207.85	$207.85	$207.80
Purchase #5	$89.50	10.336%	$98.7507	$98.75	$98.75	$98.80
Purchase #6	$107.81	3.790%	$111.896	$111.90	$111.90	$111.90
Purchase #7	$235.60	10.736%	$260.894	$260.89	$260.90	$260.90
7 purchase totals =	$1,096.90		$1,195.0267	$1,195.02	$1,195.05	$1,195.00