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	$240.87	12.437%	$270.827	$270.83	$270.85	$270.80
Purchase #2	$101.33	3.184%	$104.5563	$104.56	$104.55	$104.60
Purchase #3	$200.31	7.689%	$215.7118	$215.71	$215.70	$215.70
Purchase #4	$250.33	13.284%	$283.5838	$283.58	$283.60	$283.60
Purchase #5	$70.49	3.656%	$73.0671	$73.07	$73.05	$73.10
Purchase #6	$42.80	13.485%	$48.5716	$48.57	$48.55	$48.60
Purchase #7	$68.31	5.422%	$72.0138	$72.01	$72.00	$72.00
7 purchase totals =	$974.44		$1,068.3314	$1,068.33	$1,068.30	$1,068.40