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	$28.30	8.111%	$30.5954	$30.60	$30.60	$30.60
Purchase #2	$224.26	3.387%	$231.8557	$231.86	$231.85	$231.90
Purchase #3	$104.39	12.366%	$117.2989	$117.30	$117.30	$117.30
Purchase #4	$101.34	7.674%	$109.1168	$109.12	$109.10	$109.10
Purchase #5	$35.77	8.540%	$38.8248	$38.82	$38.80	$38.80
Purchase #6	$109.54	4.293%	$114.2426	$114.24	$114.25	$114.20
Purchase #7	$92.69	8.234%	$100.3221	$100.32	$100.30	$100.30
7 purchase totals =	$696.29		$742.2563	$742.26	$742.20	$742.20