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	$134.77	3.470%	$139.4465	$139.45	$139.45	$139.40
Purchase #2	$81.98	9.409%	$89.6935	$89.69	$89.70	$89.70
Purchase #3	$225.26	9.383%	$246.3961	$246.40	$246.40	$246.40
Purchase #4	$118.32	3.186%	$122.0897	$122.09	$122.10	$122.10
Purchase #5	$119.50	4.791%	$125.2252	$125.23	$125.25	$125.20
Purchase #6	$82.85	7.505%	$89.0679	$89.07	$89.05	$89.10
Purchase #7	$238.36	6.843%	$254.671	$254.67	$254.65	$254.70
7 purchase totals =	$1,001.04		$1,066.5899	$1,066.60	$1,066.60	$1,066.60