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	$243.39	3.371%	$251.5947	$251.59	$251.60	$251.60
Purchase #2	$175.76	8.649%	$190.9615	$190.96	$190.95	$191.00
Purchase #3	$119.92	8.724%	$130.3818	$130.38	$130.40	$130.40
Purchase #4	$142.42	10.565%	$157.4667	$157.47	$157.45	$157.50
Purchase #5	$75.40	3.811%	$78.2735	$78.27	$78.25	$78.30
Purchase #6	$116.69	9.480%	$127.7522	$127.75	$127.75	$127.80
Purchase #7	$63.83	6.544%	$68.007	$68.01	$68.00	$68.00
7 purchase totals =	$937.41		$1,004.4374	$1,004.43	$1,004.40	$1,004.60