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	$163.29	4.373%	$170.4307	$170.43	$170.45	$170.40
Purchase #2	$140.95	9.849%	$154.8322	$154.83	$154.85	$154.80
Purchase #3	$96.71	8.363%	$104.7979	$104.80	$104.80	$104.80
Purchase #4	$130.41	6.670%	$139.1083	$139.11	$139.10	$139.10
Purchase #5	$103.88	7.684%	$111.8621	$111.86	$111.85	$111.90
Purchase #6	$118.47	13.835%	$134.8603	$134.86	$134.85	$134.90
Purchase #7	$196.70	8.286%	$212.9986	$213.00	$213.00	$213.00
7 purchase totals =	$950.41		$1,028.8901	$1,028.89	$1,028.90	$1,028.90