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	$26.47	3.677%	$27.4433	$27.44	$27.45	$27.40
Purchase #2	$140.35	11.641%	$156.6881	$156.69	$156.70	$156.70
Purchase #3	$194.80	10.179%	$214.6287	$214.63	$214.65	$214.60
Purchase #4	$225.32	5.328%	$237.325	$237.33	$237.35	$237.30
Purchase #5	$176.29	11.714%	$196.9406	$196.94	$196.95	$196.90
Purchase #6	$145.47	7.137%	$155.8522	$155.85	$155.85	$155.90
Purchase #7	$88.77	3.398%	$91.7864	$91.79	$91.80	$91.80
7 purchase totals =	$997.47		$1,080.6643	$1,080.67	$1,080.75	$1,080.60