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	$150.59	11.627%	$168.0991	$168.10	$168.10	$168.10
Purchase #2	$96.50	6.109%	$102.3952	$102.40	$102.40	$102.40
Purchase #3	$163.76	7.822%	$176.5693	$176.57	$176.55	$176.60
Purchase #4	$119.60	13.755%	$136.051	$136.05	$136.05	$136.10
Purchase #5	$142.80	8.783%	$155.3421	$155.34	$155.35	$155.30
Purchase #6	$187.82	9.206%	$205.1107	$205.11	$205.10	$205.10
Purchase #7	$236.43	8.509%	$256.5478	$256.55	$256.55	$256.50
7 purchase totals =	$1,097.50		$1,200.1152	$1,200.12	$1,200.10	$1,200.10