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	$80.39	5.849%	$85.092	$85.09	$85.10	$85.10
Purchase #2	$175.48	7.484%	$188.6129	$188.61	$188.60	$188.60
Purchase #3	$171.45	3.191%	$176.921	$176.92	$176.90	$176.90
Purchase #4	$142.35	6.141%	$151.0917	$151.09	$151.10	$151.10
Purchase #5	$83.46	5.384%	$87.9535	$87.95	$87.95	$88.00
Purchase #6	$143.68	6.730%	$153.3497	$153.35	$153.35	$153.30
Purchase #7	$90.99	9.841%	$99.9443	$99.94	$99.95	$99.90
7 purchase totals =	$887.80		$942.9651	$942.95	$942.95	$942.90