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	$131.83	12.462%	$148.2587	$148.26	$148.25	$148.30
Purchase #2	$129.33	10.201%	$142.523	$142.52	$142.50	$142.50
Purchase #3	$186.93	6.203%	$198.5253	$198.53	$198.55	$198.50
Purchase #4	$132.68	6.452%	$141.2405	$141.24	$141.25	$141.20
Purchase #5	$123.68	12.398%	$139.0138	$139.01	$139.00	$139.00
Purchase #6	$37.43	12.389%	$42.0672	$42.07	$42.05	$42.10
Purchase #7	$63.89	12.722%	$72.0181	$72.02	$72.00	$72.00
7 purchase totals =	$805.77		$883.6466	$883.65	$883.60	$883.60