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	$228.40	4.719%	$239.1782	$239.18	$239.20	$239.20
Purchase #2	$127.72	6.851%	$136.4701	$136.47	$136.45	$136.50
Purchase #3	$178.86	9.535%	$195.9143	$195.91	$195.90	$195.90
Purchase #4	$137.29	3.406%	$141.9661	$141.97	$141.95	$142.00
Purchase #5	$82.77	9.380%	$90.5338	$90.53	$90.55	$90.50
Purchase #6	$177.87	4.252%	$185.433	$185.43	$185.45	$185.40
Purchase #7	$34.92	12.606%	$39.322	$39.32	$39.30	$39.30
7 purchase totals =	$967.83		$1,028.8175	$1,028.81	$1,028.80	$1,028.80