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	$41.78	3.573%	$43.2728	$43.27	$43.25	$43.30
Purchase #2	$199.27	10.768%	$220.7274	$220.73	$220.75	$220.70
Purchase #3	$113.44	11.832%	$126.8622	$126.86	$126.85	$126.90
Purchase #4	$133.92	4.479%	$139.9183	$139.92	$139.90	$139.90
Purchase #5	$155.94	6.749%	$166.4644	$166.46	$166.45	$166.50
Purchase #6	$221.75	5.291%	$233.4828	$233.48	$233.50	$233.50
Purchase #7	$220.35	3.612%	$228.309	$228.31	$228.30	$228.30
7 purchase totals =	$1,086.45		$1,159.0369	$1,159.03	$1,159.00	$1,159.10