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	$58.36	7.744%	$62.8794	$62.88	$62.90	$62.90
Purchase #2	$43.89	10.437%	$48.4708	$48.47	$48.45	$48.50
Purchase #3	$100.59	9.202%	$109.8463	$109.85	$109.85	$109.80
Purchase #4	$216.58	4.783%	$226.939	$226.94	$226.95	$226.90
Purchase #5	$85.99	9.342%	$94.0232	$94.02	$94.00	$94.00
Purchase #6	$62.27	4.732%	$65.2166	$65.22	$65.20	$65.20
Purchase #7	$53.57	7.853%	$57.7769	$57.78	$57.80	$57.80
7 purchase totals =	$621.25		$665.1522	$665.16	$665.15	$665.10