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	$240.96	11.696%	$269.1427	$269.14	$269.15	$269.10
Purchase #2	$229.94	12.258%	$258.126	$258.13	$258.15	$258.10
Purchase #3	$245.59	13.736%	$279.3242	$279.32	$279.30	$279.30
Purchase #4	$90.61	11.475%	$101.0075	$101.01	$101.00	$101.00
Purchase #5	$95.57	3.126%	$98.5575	$98.56	$98.55	$98.60
Purchase #6	$90.83	11.844%	$101.5879	$101.59	$101.60	$101.60
Purchase #7	$52.66	8.578%	$57.1772	$57.18	$57.20	$57.20
7 purchase totals =	$1,046.16		$1,164.9230	$1,164.93	$1,164.95	$1,164.90