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	$234.31	10.333%	$258.5213	$258.52	$258.50	$258.50
Purchase #2	$172.85	5.506%	$182.3671	$182.37	$182.35	$182.40
Purchase #3	$158.25	7.508%	$170.1314	$170.13	$170.15	$170.10
Purchase #4	$230.83	9.859%	$253.5875	$253.59	$253.60	$253.60
Purchase #5	$187.25	3.807%	$194.3786	$194.38	$194.40	$194.40
Purchase #6	$51.58	9.502%	$56.4811	$56.48	$56.50	$56.50
Purchase #7	$35.92	13.845%	$40.8931	$40.89	$40.90	$40.90
7 purchase totals =	$1,070.99		$1,156.3601	$1,156.36	$1,156.40	$1,156.40