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	$72.59	6.476%	$77.2909	$77.29	$77.30	$77.30
Purchase #2	$247.31	7.562%	$266.0116	$266.01	$266.00	$266.00
Purchase #3	$38.79	4.698%	$40.6124	$40.61	$40.60	$40.60
Purchase #4	$54.60	6.252%	$58.0136	$58.01	$58.00	$58.00
Purchase #5	$33.90	3.636%	$35.1326	$35.13	$35.15	$35.10
Purchase #6	$100.97	8.687%	$109.7413	$109.74	$109.75	$109.70
Purchase #7	$162.63	6.311%	$172.8936	$172.89	$172.90	$172.90
7 purchase totals =	$710.79		$759.6960	$759.68	$759.70	$759.60