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	$28.71	3.455%	$29.7019	$29.70	$29.70	$29.70
Purchase #2	$103.92	5.677%	$109.8195	$109.82	$109.80	$109.80
Purchase #3	$213.77	4.282%	$222.9236	$222.92	$222.90	$222.90
Purchase #4	$65.47	12.836%	$73.8737	$73.87	$73.85	$73.90
Purchase #5	$61.36	13.286%	$69.5123	$69.51	$69.50	$69.50
Purchase #6	$137.31	4.832%	$143.9448	$143.94	$143.95	$143.90
Purchase #7	$153.39	4.792%	$160.7404	$160.74	$160.75	$160.70
7 purchase totals =	$763.93		$810.5162	$810.50	$810.45	$810.40