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	$52.69	13.326%	$59.7115	$59.71	$59.70	$59.70
Purchase #2	$13.84	8.653%	$15.0376	$15.04	$15.05	$15.00
Purchase #3	$126.80	5.108%	$133.2769	$133.28	$133.30	$133.30
Purchase #4	$112.97	12.732%	$127.3533	$127.35	$127.35	$127.40
Purchase #5	$177.62	5.326%	$187.08	$187.08	$187.10	$187.10
Purchase #6	$103.64	5.317%	$109.1505	$109.15	$109.15	$109.20
Purchase #7	$91.92	4.690%	$96.231	$96.23	$96.25	$96.20
7 purchase totals =	$679.48		$727.8408	$727.84	$727.90	$727.90