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	$15.73	9.664%	$17.2501	$17.25	$17.25	$17.30
Purchase #2	$177.60	7.444%	$190.8205	$190.82	$190.80	$190.80
Purchase #3	$127.34	8.773%	$138.5115	$138.51	$138.50	$138.50
Purchase #4	$166.87	7.328%	$179.0982	$179.10	$179.10	$179.10
Purchase #5	$80.53	12.399%	$90.5149	$90.51	$90.50	$90.50
Purchase #6	$168.56	6.543%	$179.5889	$179.59	$179.60	$179.60
Purchase #7	$137.40	8.372%	$148.9031	$148.90	$148.90	$148.90
7 purchase totals =	$874.03		$944.6872	$944.68	$944.65	$944.70