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	$100.75	3.530%	$104.3065	$104.31	$104.30	$104.30
Purchase #2	$58.80	13.495%	$66.7351	$66.74	$66.75	$66.70
Purchase #3	$98.97	13.676%	$112.5051	$112.51	$112.50	$112.50
Purchase #4	$32.59	9.863%	$35.8044	$35.80	$35.80	$35.80
Purchase #5	$152.79	3.779%	$158.5639	$158.56	$158.55	$158.60
Purchase #6	$93.32	10.196%	$102.8349	$102.83	$102.85	$102.80
Purchase #7	$34.29	6.773%	$36.6125	$36.61	$36.60	$36.60
7 purchase totals =	$571.51		$617.3624	$617.36	$617.35	$617.30