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	$249.78	7.671%	$268.9406	$268.94	$268.95	$268.90
Purchase #2	$169.85	4.806%	$178.013	$178.01	$178.00	$178.00
Purchase #3	$42.26	11.243%	$47.0113	$47.01	$47.00	$47.00
Purchase #4	$57.77	3.656%	$59.8821	$59.88	$59.90	$59.90
Purchase #5	$131.37	6.304%	$139.6516	$139.65	$139.65	$139.70
Purchase #6	$119.88	11.159%	$133.2574	$133.26	$133.25	$133.30
Purchase #7	$243.85	11.249%	$271.2807	$271.28	$271.30	$271.30
7 purchase totals =	$1,014.76		$1,098.0367	$1,098.03	$1,098.05	$1,098.10