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	$245.33	13.131%	$277.5443	$277.54	$277.55	$277.50
Purchase #2	$165.47	13.309%	$187.4924	$187.49	$187.50	$187.50
Purchase #3	$95.65	4.746%	$100.1895	$100.19	$100.20	$100.20
Purchase #4	$165.98	3.371%	$171.5752	$171.58	$171.60	$171.60
Purchase #5	$104.99	6.233%	$111.534	$111.53	$111.55	$111.50
Purchase #6	$74.75	5.243%	$78.6691	$78.67	$78.65	$78.70
Purchase #7	$229.63	3.484%	$237.6303	$237.63	$237.65	$237.60
7 purchase totals =	$1,081.80		$1,164.6348	$1,164.63	$1,164.70	$1,164.60