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	$235.37	13.250%	$266.5565	$266.56	$266.55	$266.60
Purchase #2	$51.39	9.602%	$56.3245	$56.32	$56.30	$56.30
Purchase #3	$200.55	5.262%	$211.1029	$211.10	$211.10	$211.10
Purchase #4	$177.38	12.109%	$198.8589	$198.86	$198.85	$198.90
Purchase #5	$65.41	12.503%	$73.5882	$73.59	$73.60	$73.60
Purchase #6	$231.44	4.188%	$241.1327	$241.13	$241.15	$241.10
Purchase #7	$89.98	4.295%	$93.8446	$93.84	$93.85	$93.80
7 purchase totals =	$1,051.52		$1,141.4083	$1,141.40	$1,141.40	$1,141.40