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	$168.88	9.709%	$185.2766	$185.28	$185.30	$185.30
Purchase #2	$24.97	12.139%	$28.0011	$28.00	$28.00	$28.00
Purchase #3	$172.58	6.687%	$184.1204	$184.12	$184.10	$184.10
Purchase #4	$70.25	11.722%	$78.4847	$78.48	$78.50	$78.50
Purchase #5	$141.29	11.808%	$157.9735	$157.97	$157.95	$158.00
Purchase #6	$202.52	10.669%	$224.1269	$224.13	$224.15	$224.10
Purchase #7	$216.82	6.581%	$231.0889	$231.09	$231.10	$231.10
7 purchase totals =	$997.31		$1,089.0721	$1,089.07	$1,089.10	$1,089.10