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	$85.83	4.140%	$89.3834	$89.38	$89.40	$89.40
Purchase #2	$163.90	11.189%	$182.2388	$182.24	$182.25	$182.20
Purchase #3	$55.90	4.541%	$58.4384	$58.44	$58.45	$58.40
Purchase #4	$155.68	6.422%	$165.6778	$165.68	$165.70	$165.70
Purchase #5	$44.42	7.708%	$47.8439	$47.84	$47.85	$47.80
Purchase #6	$179.71	4.388%	$187.5957	$187.60	$187.60	$187.60
Purchase #7	$123.27	3.654%	$127.7743	$127.77	$127.75	$127.80
7 purchase totals =	$808.71		$858.9523	$858.95	$859.00	$858.90