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	$47.89	6.514%	$51.0096	$51.01	$51.00	$51.00
Purchase #2	$56.90	4.342%	$59.3706	$59.37	$59.35	$59.40
Purchase #3	$231.64	4.268%	$241.5264	$241.53	$241.55	$241.50
Purchase #4	$221.98	11.644%	$247.8274	$247.83	$247.85	$247.80
Purchase #5	$216.77	8.478%	$235.1478	$235.15	$235.15	$235.10
Purchase #6	$87.58	12.812%	$98.8007	$98.80	$98.80	$98.80
Purchase #7	$240.72	7.134%	$257.893	$257.89	$257.90	$257.90
7 purchase totals =	$1,103.48		$1,191.5755	$1,191.58	$1,191.60	$1,191.50