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	$67.74	12.268%	$76.0503	$76.05	$76.05	$76.10
Purchase #2	$57.49	3.644%	$59.5849	$59.58	$59.60	$59.60
Purchase #3	$25.70	8.335%	$27.8421	$27.84	$27.85	$27.80
Purchase #4	$100.26	3.333%	$103.6017	$103.60	$103.60	$103.60
Purchase #5	$28.76	9.528%	$31.5003	$31.50	$31.50	$31.50
Purchase #6	$211.50	9.624%	$231.8548	$231.85	$231.85	$231.90
Purchase #7	$233.27	3.425%	$241.2595	$241.26	$241.25	$241.30
7 purchase totals =	$724.72		$771.6936	$771.68	$771.70	$771.80