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	$124.27	12.228%	$139.4657	$139.47	$139.45	$139.50
Purchase #2	$182.37	12.440%	$205.0568	$205.06	$205.05	$205.10
Purchase #3	$49.62	7.750%	$53.4656	$53.47	$53.45	$53.50
Purchase #4	$78.82	5.372%	$83.0542	$83.05	$83.05	$83.10
Purchase #5	$250.50	3.511%	$259.2951	$259.30	$259.30	$259.30
Purchase #6	$232.84	9.558%	$255.0948	$255.09	$255.10	$255.10
Purchase #7	$30.44	9.312%	$33.2746	$33.27	$33.25	$33.30
7 purchase totals =	$948.86		$1,028.7068	$1,028.71	$1,028.65	$1,028.90