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	$115.49	13.674%	$131.2821	$131.28	$131.30	$131.30
Purchase #2	$71.37	9.137%	$77.8911	$77.89	$77.90	$77.90
Purchase #3	$199.52	13.855%	$227.1635	$227.16	$227.15	$227.20
Purchase #4	$45.26	8.214%	$48.9777	$48.98	$49.00	$49.00
Purchase #5	$92.86	9.783%	$101.9445	$101.94	$101.95	$101.90
Purchase #6	$134.36	11.853%	$150.2857	$150.29	$150.30	$150.30
Purchase #7	$78.42	10.428%	$86.5976	$86.60	$86.60	$86.60
7 purchase totals =	$737.28		$824.1422	$824.14	$824.20	$824.20