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	$164.98	3.712%	$171.1041	$171.10	$171.10	$171.10
Purchase #2	$180.45	8.832%	$196.3873	$196.39	$196.40	$196.40
Purchase #3	$233.25	12.711%	$262.8984	$262.90	$262.90	$262.90
Purchase #4	$161.87	13.335%	$183.4554	$183.46	$183.45	$183.50
Purchase #5	$46.60	7.186%	$49.9487	$49.95	$49.95	$49.90
Purchase #6	$70.46	11.662%	$78.677	$78.68	$78.70	$78.70
Purchase #7	$82.37	8.311%	$89.2158	$89.22	$89.20	$89.20
7 purchase totals =	$939.98		$1,031.6867	$1,031.70	$1,031.70	$1,031.70