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	$102.37	9.122%	$111.7082	$111.71	$111.70	$111.70
Purchase #2	$224.89	11.104%	$249.8618	$249.86	$249.85	$249.90
Purchase #3	$124.75	6.856%	$133.3029	$133.30	$133.30	$133.30
Purchase #4	$123.85	12.237%	$139.0055	$139.01	$139.00	$139.00
Purchase #5	$169.32	6.505%	$180.3343	$180.33	$180.35	$180.30
Purchase #6	$122.80	3.839%	$127.5143	$127.51	$127.50	$127.50
Purchase #7	$168.71	13.466%	$191.4285	$191.43	$191.45	$191.40
7 purchase totals =	$1,036.69		$1,133.1555	$1,133.15	$1,133.15	$1,133.10