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	$40.31	8.376%	$43.6864	$43.69	$43.70	$43.70
Purchase #2	$32.92	4.853%	$34.5176	$34.52	$34.50	$34.50
Purchase #3	$198.76	3.470%	$205.657	$205.66	$205.65	$205.70
Purchase #4	$118.71	11.106%	$131.8939	$131.89	$131.90	$131.90
Purchase #5	$232.35	11.620%	$259.3491	$259.35	$259.35	$259.30
Purchase #6	$135.26	9.738%	$148.4316	$148.43	$148.45	$148.40
Purchase #7	$202.38	13.340%	$229.3775	$229.38	$229.40	$229.40
7 purchase totals =	$960.69		$1,052.9131	$1,052.92	$1,052.95	$1,052.90