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	$28.71	6.209%	$30.4926	$30.49	$30.50	$30.50
Purchase #2	$89.46	10.127%	$98.5196	$98.52	$98.50	$98.50
Purchase #3	$94.38	3.111%	$97.3162	$97.32	$97.30	$97.30
Purchase #4	$10.83	8.277%	$11.7264	$11.73	$11.75	$11.70
Purchase #5	$43.83	5.134%	$46.0802	$46.08	$46.10	$46.10
Purchase #6	$143.49	3.567%	$148.6083	$148.61	$148.60	$148.60
Purchase #7	$153.41	9.832%	$168.4933	$168.49	$168.50	$168.50
7 purchase totals =	$564.11		$601.2366	$601.24	$601.25	$601.20