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	$100.83	12.659%	$113.5941	$113.59	$113.60	$113.60
Purchase #2	$126.61	12.712%	$142.7047	$142.70	$142.70	$142.70
Purchase #3	$210.27	12.293%	$236.1185	$236.12	$236.10	$236.10
Purchase #4	$138.52	12.578%	$155.943	$155.94	$155.95	$155.90
Purchase #5	$101.37	7.816%	$109.2931	$109.29	$109.30	$109.30
Purchase #6	$174.87	6.598%	$186.4079	$186.41	$186.40	$186.40
Purchase #7	$235.49	13.161%	$266.4828	$266.48	$266.50	$266.50
7 purchase totals =	$1,087.96		$1,210.5441	$1,210.53	$1,210.55	$1,210.50