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	$218.47	12.509%	$245.7984	$245.80	$245.80	$245.80
Purchase #2	$95.93	8.872%	$104.4409	$104.44	$104.45	$104.40
Purchase #3	$127.55	9.449%	$139.6022	$139.60	$139.60	$139.60
Purchase #4	$27.91	5.145%	$29.346	$29.35	$29.35	$29.30
Purchase #5	$139.47	7.855%	$150.4254	$150.43	$150.45	$150.40
Purchase #6	$114.84	7.146%	$123.0465	$123.05	$123.05	$123.00
Purchase #7	$79.89	12.358%	$89.7628	$89.76	$89.75	$89.80
7 purchase totals =	$804.06		$882.4222	$882.43	$882.45	$882.30