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	$132.45	3.609%	$137.2301	$137.23	$137.25	$137.20
Purchase #2	$185.93	3.591%	$192.6067	$192.61	$192.60	$192.60
Purchase #3	$87.28	12.698%	$98.3628	$98.36	$98.35	$98.40
Purchase #4	$36.77	6.543%	$39.1759	$39.18	$39.20	$39.20
Purchase #5	$149.69	10.476%	$165.3715	$165.37	$165.35	$165.40
Purchase #6	$70.81	10.483%	$78.233	$78.23	$78.25	$78.20
Purchase #7	$11.35	8.469%	$12.3112	$12.31	$12.30	$12.30
7 purchase totals =	$674.28		$723.2912	$723.29	$723.30	$723.30