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	$80.69	10.789%	$89.3956	$89.40	$89.40	$89.40
Purchase #2	$52.45	8.780%	$57.0551	$57.06	$57.05	$57.10
Purchase #3	$210.28	8.146%	$227.4094	$227.41	$227.40	$227.40
Purchase #4	$240.43	7.799%	$259.1811	$259.18	$259.20	$259.20
Purchase #5	$94.83	10.302%	$104.5994	$104.60	$104.60	$104.60
Purchase #6	$73.41	9.723%	$80.5477	$80.55	$80.55	$80.50
Purchase #7	$92.30	10.724%	$102.1983	$102.20	$102.20	$102.20
7 purchase totals =	$844.39		$920.3866	$920.40	$920.40	$920.40