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	$245.72	13.799%	$279.6269	$279.63	$279.65	$279.60
Purchase #2	$16.57	11.407%	$18.4601	$18.46	$18.45	$18.50
Purchase #3	$205.93	9.204%	$224.8838	$224.88	$224.90	$224.90
Purchase #4	$87.46	8.601%	$94.9824	$94.98	$95.00	$95.00
Purchase #5	$222.54	5.425%	$234.6128	$234.61	$234.60	$234.60
Purchase #6	$127.71	9.727%	$140.1324	$140.13	$140.15	$140.10
Purchase #7	$80.53	12.399%	$90.5149	$90.51	$90.50	$90.50
7 purchase totals =	$986.46		$1,083.2133	$1,083.20	$1,083.25	$1,083.20