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	$137.78	4.581%	$144.0917	$144.09	$144.10	$144.10
Purchase #2	$59.80	4.475%	$62.4761	$62.48	$62.50	$62.50
Purchase #3	$121.44	5.801%	$128.4847	$128.48	$128.50	$128.50
Purchase #4	$136.46	4.392%	$142.4533	$142.45	$142.45	$142.50
Purchase #5	$24.72	3.472%	$25.5783	$25.58	$25.60	$25.60
Purchase #6	$74.66	7.712%	$80.4178	$80.42	$80.40	$80.40
Purchase #7	$31.36	7.464%	$33.7007	$33.70	$33.70	$33.70
7 purchase totals =	$586.22		$617.2026	$617.20	$617.25	$617.30