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	$108.47	12.645%	$122.186	$122.19	$122.20	$122.20
Purchase #2	$249.52	5.330%	$262.8194	$262.82	$262.80	$262.80
Purchase #3	$133.34	6.820%	$142.4338	$142.43	$142.45	$142.40
Purchase #4	$105.27	3.731%	$109.1976	$109.20	$109.20	$109.20
Purchase #5	$156.72	7.708%	$168.8	$168.80	$168.80	$168.80
Purchase #6	$208.86	11.722%	$233.3426	$233.34	$233.35	$233.30
Purchase #7	$42.89	4.419%	$44.7853	$44.79	$44.80	$44.80
7 purchase totals =	$1,005.07		$1,083.5647	$1,083.57	$1,083.60	$1,083.50