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	$66.61	7.584%	$71.6617	$71.66	$71.65	$71.70
Purchase #2	$172.46	12.269%	$193.6191	$193.62	$193.60	$193.60
Purchase #3	$97.30	4.795%	$101.9655	$101.97	$101.95	$102.00
Purchase #4	$248.53	5.790%	$262.9199	$262.92	$262.90	$262.90
Purchase #5	$131.90	8.710%	$143.3885	$143.39	$143.40	$143.40
Purchase #6	$209.50	6.215%	$222.5204	$222.52	$222.50	$222.50
Purchase #7	$12.99	4.406%	$13.5623	$13.56	$13.55	$13.60
7 purchase totals =	$939.29		$1,009.6374	$1,009.64	$1,009.55	$1,009.70