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	$138.67	12.452%	$155.9372	$155.94	$155.95	$155.90
Purchase #2	$80.43	6.630%	$85.7625	$85.76	$85.75	$85.80
Purchase #3	$39.33	10.279%	$43.3727	$43.37	$43.35	$43.40
Purchase #4	$230.74	13.704%	$262.3606	$262.36	$262.35	$262.40
Purchase #5	$46.71	10.200%	$51.4744	$51.47	$51.45	$51.50
Purchase #6	$198.46	8.589%	$215.5057	$215.51	$215.50	$215.50
Purchase #7	$172.87	13.569%	$196.3267	$196.33	$196.35	$196.30
7 purchase totals =	$907.21		$1,010.7398	$1,010.74	$1,010.70	$1,010.80