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	$215.31	7.451%	$231.3527	$231.35	$231.35	$231.40
Purchase #2	$103.27	8.341%	$111.8838	$111.88	$111.90	$111.90
Purchase #3	$90.59	3.828%	$94.0578	$94.06	$94.05	$94.10
Purchase #4	$37.43	9.127%	$40.8462	$40.85	$40.85	$40.80
Purchase #5	$101.50	4.583%	$106.1517	$106.15	$106.15	$106.20
Purchase #6	$173.49	6.245%	$184.3245	$184.32	$184.30	$184.30
Purchase #7	$135.46	6.203%	$143.8626	$143.86	$143.85	$143.90
7 purchase totals =	$857.05		$912.4793	$912.47	$912.45	$912.60