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	$9.56	3.531%	$9.8976	$9.90	$9.90	$9.90
Purchase #2	$222.67	8.401%	$241.3765	$241.38	$241.40	$241.40
Purchase #3	$28.53	4.667%	$29.8615	$29.86	$29.85	$29.90
Purchase #4	$211.65	9.400%	$231.5451	$231.55	$231.55	$231.50
Purchase #5	$83.42	7.324%	$89.5297	$89.53	$89.55	$89.50
Purchase #6	$226.88	6.227%	$241.0078	$241.01	$241.00	$241.00
Purchase #7	$85.61	11.280%	$95.2668	$95.27	$95.25	$95.30
7 purchase totals =	$868.32		$938.4850	$938.50	$938.50	$938.50