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	$123.61	9.622%	$135.5038	$135.50	$135.50	$135.50
Purchase #2	$138.34	5.227%	$145.571	$145.57	$145.55	$145.60
Purchase #3	$159.63	4.202%	$166.3377	$166.34	$166.35	$166.30
Purchase #4	$133.65	7.229%	$143.3116	$143.31	$143.30	$143.30
Purchase #5	$33.71	13.749%	$38.3448	$38.34	$38.35	$38.30
Purchase #6	$83.96	7.184%	$89.9917	$89.99	$90.00	$90.00
Purchase #7	$196.43	11.173%	$218.3771	$218.38	$218.40	$218.40
7 purchase totals =	$869.33		$937.4377	$937.43	$937.45	$937.40