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	$89.32	12.330%	$100.3332	$100.33	$100.35	$100.30
Purchase #2	$127.57	3.360%	$131.8564	$131.86	$131.85	$131.90
Purchase #3	$7.69	12.845%	$8.6778	$8.68	$8.70	$8.70
Purchase #4	$84.31	3.670%	$87.4042	$87.40	$87.40	$87.40
Purchase #5	$69.48	4.213%	$72.4072	$72.41	$72.40	$72.40
Purchase #6	$224.93	5.152%	$236.5184	$236.52	$236.50	$236.50
Purchase #7	$14.28	8.581%	$15.5054	$15.51	$15.50	$15.50
7 purchase totals =	$617.58		$652.7026	$652.71	$652.70	$652.70