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	$232.66	10.270%	$256.5542	$256.55	$256.55	$256.60
Purchase #2	$19.90	7.675%	$21.4273	$21.43	$21.45	$21.40
Purchase #3	$7.27	4.300%	$7.5826	$7.58	$7.60	$7.60
Purchase #4	$185.75	12.750%	$209.4331	$209.43	$209.45	$209.40
Purchase #5	$186.80	5.202%	$196.5173	$196.52	$196.50	$196.50
Purchase #6	$88.69	6.150%	$94.1444	$94.14	$94.15	$94.10
Purchase #7	$77.58	9.749%	$85.1433	$85.14	$85.15	$85.10
7 purchase totals =	$798.65		$870.8022	$870.79	$870.85	$870.70