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	$67.58	6.745%	$72.1383	$72.14	$72.15	$72.10
Purchase #2	$221.77	4.380%	$231.4835	$231.48	$231.50	$231.50
Purchase #3	$99.90	3.336%	$103.2327	$103.23	$103.25	$103.20
Purchase #4	$66.66	11.346%	$74.2232	$74.22	$74.20	$74.20
Purchase #5	$65.31	13.686%	$74.2483	$74.25	$74.25	$74.20
Purchase #6	$92.52	12.523%	$104.1063	$104.11	$104.10	$104.10
Purchase #7	$173.61	5.219%	$182.6707	$182.67	$182.65	$182.70
7 purchase totals =	$787.35		$842.1030	$842.10	$842.10	$842.00