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	$16.70	5.349%	$17.5933	$17.59	$17.60	$17.60
Purchase #2	$84.83	8.379%	$91.9379	$91.94	$91.95	$91.90
Purchase #3	$156.83	10.314%	$173.0054	$173.01	$173.00	$173.00
Purchase #4	$149.56	3.362%	$154.5882	$154.59	$154.60	$154.60
Purchase #5	$37.92	7.527%	$40.7742	$40.77	$40.75	$40.80
Purchase #6	$35.83	10.870%	$39.7247	$39.72	$39.70	$39.70
Purchase #7	$85.63	5.345%	$90.2069	$90.21	$90.20	$90.20
7 purchase totals =	$567.30		$607.8306	$607.83	$607.80	$607.80