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	$109.67	12.191%	$123.0399	$123.04	$123.05	$123.00
Purchase #2	$209.53	10.550%	$231.6354	$231.64	$231.65	$231.60
Purchase #3	$189.61	13.187%	$214.6139	$214.61	$214.60	$214.60
Purchase #4	$98.72	5.722%	$104.3688	$104.37	$104.35	$104.40
Purchase #5	$158.95	10.107%	$175.0151	$175.02	$175.00	$175.00
Purchase #6	$157.53	9.780%	$172.9364	$172.94	$172.95	$172.90
Purchase #7	$55.86	13.862%	$63.6033	$63.60	$63.60	$63.60
7 purchase totals =	$979.87		$1,085.2128	$1,085.22	$1,085.20	$1,085.10