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	$241.53	11.869%	$270.1972	$270.20	$270.20	$270.20
Purchase #2	$232.29	4.476%	$242.6873	$242.69	$242.70	$242.70
Purchase #3	$55.30	11.289%	$61.5428	$61.54	$61.55	$61.50
Purchase #4	$95.64	7.458%	$102.7728	$102.77	$102.75	$102.80
Purchase #5	$126.96	13.110%	$143.6045	$143.60	$143.60	$143.60
Purchase #6	$244.31	4.570%	$255.475	$255.48	$255.50	$255.50
Purchase #7	$56.85	6.589%	$60.5958	$60.60	$60.60	$60.60
7 purchase totals =	$1,052.88		$1,136.8754	$1,136.88	$1,136.90	$1,136.90