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	$177.49	7.578%	$190.9402	$190.94	$190.95	$190.90
Purchase #2	$41.33	3.551%	$42.7976	$42.80	$42.80	$42.80
Purchase #3	$143.54	9.191%	$156.7328	$156.73	$156.75	$156.70
Purchase #4	$87.39	5.174%	$91.9116	$91.91	$91.90	$91.90
Purchase #5	$48.58	8.120%	$52.5247	$52.52	$52.50	$52.50
Purchase #6	$10.57	11.618%	$11.798	$11.80	$11.80	$11.80
Purchase #7	$103.38	8.591%	$112.2614	$112.26	$112.25	$112.30
7 purchase totals =	$612.28		$658.9663	$658.96	$658.95	$658.90