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	$117.85	13.536%	$133.8022	$133.80	$133.80	$133.80
Purchase #2	$250.67	3.333%	$259.0248	$259.02	$259.00	$259.00
Purchase #3	$84.39	9.622%	$92.51	$92.51	$92.50	$92.50
Purchase #4	$6.76	8.367%	$7.3256	$7.33	$7.35	$7.30
Purchase #5	$70.82	10.597%	$78.3248	$78.32	$78.30	$78.30
Purchase #6	$20.91	9.432%	$22.8822	$22.88	$22.90	$22.90
Purchase #7	$38.76	7.328%	$41.6003	$41.60	$41.60	$41.60
7 purchase totals =	$590.16		$635.4699	$635.46	$635.45	$635.40