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	$224.55	7.368%	$241.0948	$241.09	$241.10	$241.10
Purchase #2	$125.66	12.590%	$141.4806	$141.48	$141.50	$141.50
Purchase #3	$97.38	6.621%	$103.8275	$103.83	$103.85	$103.80
Purchase #4	$114.50	3.294%	$118.2716	$118.27	$118.25	$118.30
Purchase #5	$52.51	13.363%	$59.5269	$59.53	$59.55	$59.50
Purchase #6	$22.97	12.629%	$25.8709	$25.87	$25.85	$25.90
Purchase #7	$140.72	13.819%	$160.1661	$160.17	$160.15	$160.20
7 purchase totals =	$778.29		$850.2384	$850.24	$850.25	$850.30