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	$24.51	12.371%	$27.5421	$27.54	$27.55	$27.50
Purchase #2	$104.37	8.294%	$113.0264	$113.03	$113.05	$113.00
Purchase #3	$123.34	3.715%	$127.9221	$127.92	$127.90	$127.90
Purchase #4	$119.83	4.840%	$125.6298	$125.63	$125.65	$125.60
Purchase #5	$110.42	9.216%	$120.5963	$120.60	$120.60	$120.60
Purchase #6	$129.48	9.117%	$141.2847	$141.28	$141.30	$141.30
Purchase #7	$96.32	13.647%	$109.4648	$109.46	$109.45	$109.50
7 purchase totals =	$708.27		$765.4662	$765.46	$765.50	$765.40