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	$241.27	13.297%	$273.3517	$273.35	$273.35	$273.40
Purchase #2	$211.29	4.335%	$220.4494	$220.45	$220.45	$220.40
Purchase #3	$120.90	6.191%	$128.3849	$128.38	$128.40	$128.40
Purchase #4	$171.85	10.251%	$189.4663	$189.47	$189.45	$189.50
Purchase #5	$192.47	12.531%	$216.5884	$216.59	$216.60	$216.60
Purchase #6	$108.90	9.618%	$119.374	$119.37	$119.35	$119.40
Purchase #7	$142.73	7.537%	$153.4876	$153.49	$153.50	$153.50
7 purchase totals =	$1,189.41		$1,301.1023	$1,301.10	$1,301.10	$1,301.20