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	$179.55	3.188%	$185.2741	$185.27	$185.25	$185.30
Purchase #2	$162.40	13.789%	$184.7933	$184.79	$184.80	$184.80
Purchase #3	$219.27	9.800%	$240.7585	$240.76	$240.75	$240.80
Purchase #4	$132.72	13.474%	$150.6027	$150.60	$150.60	$150.60
Purchase #5	$214.94	12.115%	$240.98	$240.98	$241.00	$241.00
Purchase #6	$208.91	10.639%	$231.1359	$231.14	$231.15	$231.10
Purchase #7	$205.59	4.641%	$215.1314	$215.13	$215.15	$215.10
7 purchase totals =	$1,323.38		$1,448.6759	$1,448.67	$1,448.70	$1,448.70