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	$45.66	7.524%	$49.0955	$49.10	$49.10	$49.10
Purchase #2	$121.92	11.563%	$136.0176	$136.02	$136.00	$136.00
Purchase #3	$128.39	4.788%	$134.5373	$134.54	$134.55	$134.50
Purchase #4	$226.73	9.610%	$248.5188	$248.52	$248.50	$248.50
Purchase #5	$172.92	6.609%	$184.3483	$184.35	$184.35	$184.30
Purchase #6	$100.81	3.287%	$104.1236	$104.12	$104.10	$104.10
Purchase #7	$144.86	4.202%	$150.947	$150.95	$150.95	$150.90
7 purchase totals =	$941.29		$1,007.5881	$1,007.60	$1,007.55	$1,007.40