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	$89.70	4.371%	$93.6208	$93.62	$93.60	$93.60
Purchase #2	$134.34	13.507%	$152.4853	$152.49	$152.50	$152.50
Purchase #3	$104.77	6.680%	$111.7686	$111.77	$111.75	$111.80
Purchase #4	$80.76	11.444%	$90.0022	$90.00	$90.00	$90.00
Purchase #5	$102.47	5.161%	$107.7585	$107.76	$107.75	$107.80
Purchase #6	$169.25	10.750%	$187.4444	$187.44	$187.45	$187.40
Purchase #7	$165.96	12.502%	$186.7083	$186.71	$186.70	$186.70
7 purchase totals =	$847.25		$929.7881	$929.79	$929.75	$929.80