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	$74.76	10.636%	$82.7115	$82.71	$82.70	$82.70
Purchase #2	$87.60	4.307%	$91.3729	$91.37	$91.35	$91.40
Purchase #3	$140.31	3.259%	$144.8827	$144.88	$144.90	$144.90
Purchase #4	$53.89	10.262%	$59.4202	$59.42	$59.40	$59.40
Purchase #5	$125.43	6.758%	$133.9066	$133.91	$133.90	$133.90
Purchase #6	$129.41	11.614%	$144.4397	$144.44	$144.45	$144.40
Purchase #7	$58.83	8.357%	$63.7464	$63.75	$63.75	$63.70
7 purchase totals =	$670.23		$720.4800	$720.48	$720.45	$720.40