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	$167.90	3.831%	$174.3322	$174.33	$174.35	$174.30
Purchase #2	$107.53	8.663%	$116.8453	$116.85	$116.85	$116.80
Purchase #3	$163.78	5.815%	$173.3038	$173.30	$173.30	$173.30
Purchase #4	$103.47	9.622%	$113.4259	$113.43	$113.45	$113.40
Purchase #5	$59.73	12.118%	$66.9681	$66.97	$66.95	$67.00
Purchase #6	$42.85	4.722%	$44.8734	$44.87	$44.85	$44.90
Purchase #7	$220.91	13.417%	$250.5495	$250.55	$250.55	$250.50
7 purchase totals =	$866.17		$940.2982	$940.30	$940.30	$940.20