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	$136.29	5.832%	$144.2384	$144.24	$144.25	$144.20
Purchase #2	$136.55	5.586%	$144.1777	$144.18	$144.20	$144.20
Purchase #3	$170.71	9.258%	$186.5143	$186.51	$186.50	$186.50
Purchase #4	$142.63	5.536%	$150.526	$150.53	$150.55	$150.50
Purchase #5	$157.30	9.725%	$172.5974	$172.60	$172.60	$172.60
Purchase #6	$118.92	8.243%	$128.7226	$128.72	$128.70	$128.70
Purchase #7	$223.63	13.408%	$253.6143	$253.61	$253.60	$253.60
7 purchase totals =	$1,086.03		$1,180.3907	$1,180.39	$1,180.40	$1,180.30