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	$80.91	8.136%	$87.4928	$87.49	$87.50	$87.50
Purchase #2	$218.33	3.708%	$226.4257	$226.43	$226.45	$226.40
Purchase #3	$237.66	5.371%	$250.4247	$250.42	$250.40	$250.40
Purchase #4	$123.83	11.556%	$138.1398	$138.14	$138.15	$138.10
Purchase #5	$114.70	11.198%	$127.5441	$127.54	$127.55	$127.50
Purchase #6	$170.54	11.550%	$190.2374	$190.24	$190.25	$190.20
Purchase #7	$168.67	4.425%	$176.1336	$176.13	$176.15	$176.10
7 purchase totals =	$1,114.64		$1,196.3981	$1,196.39	$1,196.45	$1,196.20