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	$202.92	10.431%	$224.0866	$224.09	$224.10	$224.10
Purchase #2	$40.81	3.189%	$42.1114	$42.11	$42.10	$42.10
Purchase #3	$132.90	9.811%	$145.9388	$145.94	$145.95	$145.90
Purchase #4	$228.77	10.800%	$253.4772	$253.48	$253.50	$253.50
Purchase #5	$9.89	4.311%	$10.3164	$10.32	$10.30	$10.30
Purchase #6	$99.48	9.804%	$109.233	$109.23	$109.25	$109.20
Purchase #7	$51.73	4.214%	$53.9099	$53.91	$53.90	$53.90
7 purchase totals =	$766.50		$839.0733	$839.08	$839.10	$839.00