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	$103.60	6.484%	$110.3174	$110.32	$110.30	$110.30
Purchase #2	$175.93	11.631%	$196.3924	$196.39	$196.40	$196.40
Purchase #3	$25.95	4.514%	$27.1214	$27.12	$27.10	$27.10
Purchase #4	$95.47	13.633%	$108.4854	$108.49	$108.50	$108.50
Purchase #5	$131.90	8.491%	$143.0996	$143.10	$143.10	$143.10
Purchase #6	$5.38	10.387%	$5.9388	$5.94	$5.95	$5.90
Purchase #7	$223.96	10.520%	$247.5206	$247.52	$247.50	$247.50
7 purchase totals =	$762.19		$838.8756	$838.88	$838.85	$838.80