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	$125.67	10.333%	$138.6555	$138.66	$138.65	$138.70
Purchase #2	$237.77	8.571%	$258.1493	$258.15	$258.15	$258.10
Purchase #3	$176.33	5.756%	$186.4796	$186.48	$186.50	$186.50
Purchase #4	$190.74	7.291%	$204.6469	$204.65	$204.65	$204.60
Purchase #5	$113.85	11.649%	$127.1124	$127.11	$127.10	$127.10
Purchase #6	$100.59	5.803%	$106.4272	$106.43	$106.45	$106.40
Purchase #7	$71.95	9.745%	$78.9615	$78.96	$78.95	$79.00
7 purchase totals =	$1,016.90		$1,100.4324	$1,100.44	$1,100.45	$1,100.40