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	$221.38	8.428%	$240.0379	$240.04	$240.05	$240.00
Purchase #2	$42.27	11.596%	$47.1716	$47.17	$47.15	$47.20
Purchase #3	$59.92	3.360%	$61.9333	$61.93	$61.95	$61.90
Purchase #4	$184.26	6.647%	$196.5078	$196.51	$196.50	$196.50
Purchase #5	$191.82	4.235%	$199.9436	$199.94	$199.95	$199.90
Purchase #6	$198.61	13.392%	$225.2079	$225.21	$225.20	$225.20
Purchase #7	$14.32	7.308%	$15.3665	$15.37	$15.35	$15.40
7 purchase totals =	$912.58		$986.1686	$986.17	$986.15	$986.10