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	$40.25	4.206%	$41.9429	$41.94	$41.95	$41.90
Purchase #2	$13.42	13.203%	$15.1918	$15.19	$15.20	$15.20
Purchase #3	$82.65	8.790%	$89.9149	$89.91	$89.90	$89.90
Purchase #4	$93.59	9.334%	$102.3257	$102.33	$102.35	$102.30
Purchase #5	$101.32	9.780%	$111.2291	$111.23	$111.25	$111.20
Purchase #6	$17.43	12.409%	$19.5929	$19.59	$19.60	$19.60
Purchase #7	$215.32	7.134%	$230.6809	$230.68	$230.70	$230.70
7 purchase totals =	$563.98		$610.8782	$610.87	$610.95	$610.80