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	$215.39	12.576%	$242.4774	$242.48	$242.50	$242.50
Purchase #2	$137.36	13.859%	$156.3967	$156.40	$156.40	$156.40
Purchase #3	$113.59	3.436%	$117.493	$117.49	$117.50	$117.50
Purchase #4	$10.81	5.196%	$11.3717	$11.37	$11.35	$11.40
Purchase #5	$128.53	6.279%	$136.6004	$136.60	$136.60	$136.60
Purchase #6	$223.65	12.493%	$251.5906	$251.59	$251.60	$251.60
Purchase #7	$228.55	9.440%	$250.1251	$250.13	$250.15	$250.10
7 purchase totals =	$1,057.88		$1,166.0549	$1,166.06	$1,166.10	$1,166.10