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	$220.63	12.523%	$248.2595	$248.26	$248.25	$248.30
Purchase #2	$77.68	9.713%	$85.2251	$85.23	$85.25	$85.20
Purchase #3	$91.69	12.438%	$103.0944	$103.09	$103.10	$103.10
Purchase #4	$160.56	8.630%	$174.4163	$174.42	$174.40	$174.40
Purchase #5	$159.37	3.284%	$164.6037	$164.60	$164.60	$164.60
Purchase #6	$79.88	13.810%	$90.9114	$90.91	$90.90	$90.90
Purchase #7	$217.96	10.792%	$241.4822	$241.48	$241.50	$241.50
7 purchase totals =	$1,007.77		$1,107.9926	$1,107.99	$1,108.00	$1,108.00