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	$80.48	12.404%	$90.4627	$90.46	$90.45	$90.50
Purchase #2	$227.71	13.442%	$258.3188	$258.32	$258.30	$258.30
Purchase #3	$176.88	11.148%	$196.5986	$196.60	$196.60	$196.60
Purchase #4	$35.37	8.801%	$38.4829	$38.48	$38.50	$38.50
Purchase #5	$115.71	12.379%	$130.0337	$130.03	$130.05	$130.00
Purchase #6	$156.47	3.618%	$162.1311	$162.13	$162.15	$162.10
Purchase #7	$235.47	12.693%	$265.3582	$265.36	$265.35	$265.40
7 purchase totals =	$1,028.09		$1,141.3860	$1,141.38	$1,141.40	$1,141.40