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	$19.69	11.800%	$22.0134	$22.01	$22.00	$22.00
Purchase #2	$64.28	12.498%	$72.3137	$72.31	$72.30	$72.30
Purchase #3	$112.33	11.169%	$124.8761	$124.88	$124.90	$124.90
Purchase #4	$80.29	13.210%	$90.8963	$90.90	$90.90	$90.90
Purchase #5	$187.47	9.408%	$205.1072	$205.11	$205.10	$205.10
Purchase #6	$116.94	9.828%	$128.4329	$128.43	$128.45	$128.40
Purchase #7	$26.32	11.372%	$29.3131	$29.31	$29.30	$29.30
7 purchase totals =	$607.32		$672.9527	$672.95	$672.95	$672.90