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	$35.70	13.110%	$40.3803	$40.38	$40.40	$40.40
Purchase #2	$93.62	5.837%	$99.0846	$99.08	$99.10	$99.10
Purchase #3	$210.90	5.394%	$222.2759	$222.28	$222.30	$222.30
Purchase #4	$22.91	11.600%	$25.5676	$25.57	$25.55	$25.60
Purchase #5	$200.92	13.138%	$227.3169	$227.32	$227.30	$227.30
Purchase #6	$240.47	6.285%	$255.5835	$255.58	$255.60	$255.60
Purchase #7	$70.32	9.809%	$77.2177	$77.22	$77.20	$77.20
7 purchase totals =	$874.84		$947.4265	$947.43	$947.45	$947.50