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	$50.47	12.216%	$56.6354	$56.64	$56.65	$56.60
Purchase #2	$56.51	4.546%	$59.0789	$59.08	$59.10	$59.10
Purchase #3	$55.61	13.572%	$63.1574	$63.16	$63.15	$63.20
Purchase #4	$162.34	10.390%	$179.2071	$179.21	$179.20	$179.20
Purchase #5	$100.88	12.861%	$113.8542	$113.85	$113.85	$113.90
Purchase #6	$99.25	10.482%	$109.6534	$109.65	$109.65	$109.70
Purchase #7	$237.30	11.760%	$265.2065	$265.21	$265.20	$265.20
7 purchase totals =	$762.36		$846.7929	$846.80	$846.80	$846.90