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	$136.57	6.508%	$145.458	$145.46	$145.45	$145.50
Purchase #2	$101.93	9.544%	$111.6582	$111.66	$111.65	$111.70
Purchase #3	$52.25	3.701%	$54.1838	$54.18	$54.20	$54.20
Purchase #4	$187.48	12.523%	$210.9581	$210.96	$210.95	$211.00
Purchase #5	$237.90	5.364%	$250.661	$250.66	$250.65	$250.70
Purchase #6	$121.30	8.191%	$131.2357	$131.24	$131.25	$131.20
Purchase #7	$50.25	9.576%	$55.0619	$55.06	$55.05	$55.10
7 purchase totals =	$887.68		$959.2167	$959.22	$959.20	$959.40