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	$112.76	13.446%	$127.9217	$127.92	$127.90	$127.90
Purchase #2	$38.93	6.719%	$41.5457	$41.55	$41.55	$41.50
Purchase #3	$231.72	4.177%	$241.3989	$241.40	$241.40	$241.40
Purchase #4	$128.79	13.480%	$146.1509	$146.15	$146.15	$146.20
Purchase #5	$152.70	4.424%	$159.4554	$159.46	$159.45	$159.50
Purchase #6	$177.34	6.227%	$188.383	$188.38	$188.40	$188.40
Purchase #7	$48.57	7.398%	$52.1632	$52.16	$52.15	$52.20
7 purchase totals =	$890.81		$957.0188	$957.02	$957.00	$957.10