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	$122.68	11.187%	$136.4042	$136.40	$136.40	$136.40
Purchase #2	$112.37	13.650%	$127.7085	$127.71	$127.70	$127.70
Purchase #3	$98.79	13.383%	$112.0111	$112.01	$112.00	$112.00
Purchase #4	$113.58	11.841%	$127.029	$127.03	$127.05	$127.00
Purchase #5	$165.99	12.349%	$186.4881	$186.49	$186.50	$186.50
Purchase #6	$246.43	4.443%	$257.3789	$257.38	$257.40	$257.40
Purchase #7	$29.54	12.581%	$33.2564	$33.26	$33.25	$33.30
7 purchase totals =	$889.38		$980.2762	$980.28	$980.30	$980.30