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	$35.35	13.347%	$40.0682	$40.07	$40.05	$40.10
Purchase #2	$221.73	6.356%	$235.8232	$235.82	$235.80	$235.80
Purchase #3	$81.53	9.620%	$89.3732	$89.37	$89.35	$89.40
Purchase #4	$38.79	5.868%	$41.0662	$41.07	$41.05	$41.10
Purchase #5	$150.31	11.567%	$167.6964	$167.70	$167.70	$167.70
Purchase #6	$82.32	7.480%	$88.4775	$88.48	$88.50	$88.50
Purchase #7	$73.89	8.670%	$80.2963	$80.30	$80.30	$80.30
7 purchase totals =	$683.92		$742.8010	$742.81	$742.75	$742.90