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	$99.32	13.105%	$112.3359	$112.34	$112.35	$112.30
Purchase #2	$137.80	9.466%	$150.8441	$150.84	$150.85	$150.80
Purchase #3	$128.46	11.410%	$143.1173	$143.12	$143.10	$143.10
Purchase #4	$26.30	11.630%	$29.3587	$29.36	$29.35	$29.40
Purchase #5	$127.60	10.167%	$140.5731	$140.57	$140.55	$140.60
Purchase #6	$46.53	12.425%	$52.3114	$52.31	$52.30	$52.30
Purchase #7	$98.88	10.522%	$109.2842	$109.28	$109.30	$109.30
7 purchase totals =	$664.89		$737.8247	$737.82	$737.80	$737.80