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	$220.94	12.482%	$248.5177	$248.52	$248.50	$248.50
Purchase #2	$171.33	4.436%	$178.9302	$178.93	$178.95	$178.90
Purchase #3	$246.94	6.487%	$262.959	$262.96	$262.95	$263.00
Purchase #4	$127.39	9.479%	$139.4653	$139.47	$139.45	$139.50
Purchase #5	$142.96	6.528%	$152.2924	$152.29	$152.30	$152.30
Purchase #6	$35.57	8.254%	$38.5059	$38.51	$38.50	$38.50
Purchase #7	$62.79	9.732%	$68.9007	$68.90	$68.90	$68.90
7 purchase totals =	$1,007.92		$1,089.5712	$1,089.58	$1,089.55	$1,089.60