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	$42.37	13.660%	$48.1577	$48.16	$48.15	$48.20
Purchase #2	$96.59	13.351%	$109.4857	$109.49	$109.50	$109.50
Purchase #3	$10.54	10.229%	$11.6181	$11.62	$11.60	$11.60
Purchase #4	$203.90	5.575%	$215.2674	$215.27	$215.25	$215.30
Purchase #5	$44.76	4.747%	$46.8848	$46.88	$46.90	$46.90
Purchase #6	$196.81	9.808%	$216.1131	$216.11	$216.10	$216.10
Purchase #7	$39.90	3.209%	$41.1804	$41.18	$41.20	$41.20
7 purchase totals =	$634.87		$688.7072	$688.71	$688.70	$688.80