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	$83.54	12.720%	$94.1663	$94.17	$94.15	$94.20
Purchase #2	$220.47	7.867%	$237.8144	$237.81	$237.80	$237.80
Purchase #3	$88.60	13.167%	$100.266	$100.27	$100.25	$100.30
Purchase #4	$176.86	4.271%	$184.4137	$184.41	$184.40	$184.40
Purchase #5	$78.67	4.742%	$82.4005	$82.40	$82.40	$82.40
Purchase #6	$73.77	9.565%	$80.8261	$80.83	$80.85	$80.80
Purchase #7	$92.53	3.369%	$95.6473	$95.65	$95.65	$95.60
7 purchase totals =	$814.44		$875.5343	$875.54	$875.50	$875.50