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	$99.50	9.226%	$108.6799	$108.68	$108.70	$108.70
Purchase #2	$38.61	10.412%	$42.6301	$42.63	$42.65	$42.60
Purchase #3	$184.46	6.636%	$196.7008	$196.70	$196.70	$196.70
Purchase #4	$133.31	8.742%	$144.964	$144.96	$144.95	$145.00
Purchase #5	$52.75	11.476%	$58.8036	$58.80	$58.80	$58.80
Purchase #6	$200.63	7.388%	$215.4525	$215.45	$215.45	$215.50
Purchase #7	$127.92	11.196%	$142.2419	$142.24	$142.25	$142.20
7 purchase totals =	$837.18		$909.4728	$909.46	$909.50	$909.50