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	$71.27	9.739%	$78.211	$78.21	$78.20	$78.20
Purchase #2	$159.31	5.383%	$167.8857	$167.89	$167.90	$167.90
Purchase #3	$72.96	8.610%	$79.2419	$79.24	$79.25	$79.20
Purchase #4	$79.82	6.396%	$84.9253	$84.93	$84.95	$84.90
Purchase #5	$127.89	13.757%	$145.4838	$145.48	$145.50	$145.50
Purchase #6	$241.37	13.121%	$273.0402	$273.04	$273.05	$273.00
Purchase #7	$106.72	5.223%	$112.294	$112.29	$112.30	$112.30
7 purchase totals =	$859.34		$941.0819	$941.08	$941.15	$941.00