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	$37.58	5.825%	$39.769	$39.77	$39.75	$39.80
Purchase #2	$61.98	3.318%	$64.0365	$64.04	$64.05	$64.00
Purchase #3	$159.30	11.394%	$177.4506	$177.45	$177.45	$177.50
Purchase #4	$41.48	4.222%	$43.2313	$43.23	$43.25	$43.20
Purchase #5	$150.31	12.152%	$168.5757	$168.58	$168.60	$168.60
Purchase #6	$32.70	8.850%	$35.594	$35.59	$35.60	$35.60
Purchase #7	$87.34	13.683%	$99.2907	$99.29	$99.30	$99.30
7 purchase totals =	$570.69		$627.9478	$627.95	$628.00	$628.00