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	$155.73	3.268%	$160.8193	$160.82	$160.80	$160.80
Purchase #2	$45.50	9.826%	$49.9708	$49.97	$49.95	$50.00
Purchase #3	$74.41	10.862%	$82.4924	$82.49	$82.50	$82.50
Purchase #4	$154.99	10.737%	$171.6313	$171.63	$171.65	$171.60
Purchase #5	$131.38	9.439%	$143.781	$143.78	$143.80	$143.80
Purchase #6	$47.43	3.476%	$49.0787	$49.08	$49.10	$49.10
Purchase #7	$139.39	3.600%	$144.408	$144.41	$144.40	$144.40
7 purchase totals =	$748.83		$802.1815	$802.18	$802.20	$802.20