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	$215.93	12.477%	$242.8716	$242.87	$242.85	$242.90
Purchase #2	$87.61	4.452%	$91.5104	$91.51	$91.50	$91.50
Purchase #3	$174.86	8.821%	$190.2844	$190.28	$190.30	$190.30
Purchase #4	$16.48	13.282%	$18.6689	$18.67	$18.65	$18.70
Purchase #5	$37.51	11.392%	$41.7831	$41.78	$41.80	$41.80
Purchase #6	$7.45	11.314%	$8.2929	$8.29	$8.30	$8.30
Purchase #7	$39.58	7.187%	$42.4246	$42.42	$42.40	$42.40
7 purchase totals =	$579.42		$635.8359	$635.82	$635.80	$635.90